Dude you are the man. Giving the most in depth explain actions of Holley carbs of ANY video I’ve ever watched trying to understand them. I recently did a 5.0 swap on an 88 Ford ranger using a 302 out in an 89 fox body, converted from EFI to Holley street warrior 600 just because I wanted old school simplicity of no sensors to worry about. Turns out tuning the carb to run the way it should isn’t so simple if you don’t understand them. I was just about to pay a guy to tune it for me until I found your videos, now I’m highly considering doing it myself!
Thanks man, trust me when I say most of those carb "tuners" only understand the basics. They will set your timing, idle and maybe jetting but thats where it ends. A drivability tune takes a lot of time to get 100% and no 2 cars are the same. You'll get frustrated, but by the time you're done, theres nothing better.
@@NightWrencher one question I have is about vacuume secondaries. I don’t think mine are opening even with the lightest spring in the diaphragm. Could that be due to jet/power valve tuning or is it simply because it’s running with a manual transmission? I’ve read that vacuume secondary is best suited for an automatic trans because the motor is under more of a load to generate more vacuume but I figure if I’m stomping on the gas in 2nd-3rd gear those secondaries should be engaging.
It don’t take much to get the truck moving, big HP to weight ratio, but it should have more pickup in the higher gears than it has IMO. Acts like it’s still running on 2 barrels when I stab it in the higher gears starting from about 2k RPMS
Have you tried the paper clip trick to see if they are actually opening? regardless of engine size, the secondaries should open once the throttle is opened far enough.
The Metering Block Idle Feed Restriction and the Main Body Idle Air Bleed make an emulsion that feeds both the round Curb Idle Discharge Hole AND the Transfer Slot... The Idle Mixture Screw adjust the amount of Idle Emulsion delivered out of the round curb idle discharge hole. The Transfer Slot is fed from the same Idle Well, BUT the Transfer Slot Feed is UPSTREAM of the Idle Mixture Screw, so it 'robs' all the emulsion from the round Curb Idle discharge hole IF the Transfer Slot is over exposed and control of the idle mixture discharge from the round curb idle discharge hole by way of the mixture Screw is lost IF the Transfer Slot is over exposed. Does that make sense?
I just replied to Nightwrencher; "My carb won't idle at all. 350 CI SBC with mild performance Lunati cam. Carb is a 650 double pumper with 4 idle circuits. After fixing two leaks, (front Accelerator pump housing and stripped rear bowl screw), it would not idle and just died unless I opened the throttle plates a lot. Also my idle vacuum that was 19 in hg at 750 rpm is now 15 in hg. I had to ask myself what did I change? All new gaskets, new needle cork seals, new needle and seats. But, I later remembered that I had put some silicon grease on the needles and seals to help them go in. That's the only thing different from a normal rebuild, that I did. I now honestly think that the silicon grease and non ethanol gas plus octane booster I run, somehow formed some chunks or goo that clogged the idle restrictors in the metering blocks. So I did a super clean out of all passages but that still didn't fix the problem. I can adjust the screws in to the stops but it still runs, but rough. Probably because it's running on the transfer slots since the idle stop is so far open. I ordered new metering blocks yesterday and will find out if that is the problem. I hope it is because I'm running out of ideas. Great informational video, thank you." Olsketchmo; Your explanation of the idle circuit and transfer slots is really great information. I thought I knew a lot about Holleys, now I know more. Thank you.
Why is definitely important: control of idle mixture fades the more slot is exposed - they compete from the same fuel well in the metering block, and... transfer slot is closer to the source. When throttle opens to expose all the transfer slot, the idle mixture screw port sees a nearly equalized signal on either side and idle port flow suffers. You did the right thing tuning by vacuum: it reveals the quality of tune like clockwork.
Thanks for an excellent explanation of properly setting up the Idle and Transition circuit on a Holley. I like it that you have mentioned some of the problems of the circuits and what they do as well as how to fix them in a procedural way.
@@NightWrencher good stuff. You did miss one very important thing with more high performance/race type engines. Throttle blade air bypass hole. Basically similar thing, hot w/ idle/air... close Just keep drilling the bypass holes in all throttle blades until it idles in the neighborhood of where you want it to. Race engines with bigger cams wont idle w/o that and people go cranking on that idle screw, get into the transfer slot and have a mad hesitation, try and crutch... Fairly simple thing. Once you know where you need to be, you can order throttle blades with the right size hole when you set out to build a carb for a similar application. The Holley Ultra XP has a different bypass by the air cleaner stud, but not everyone runs that. More than okay with no videos covering this 😅🤫
I got a bunch of them from a guy out in Kentuckey. HPR Carbs, his name is Johnathan. Sells all kinds of new and used holley parts at a good price. Look him up on facebook
I have a Holley Speed Demon 750DP carb that I can't get to drive at low speeds about 20 or 25MPH cruising the neighborhood it goes lean about 20 + AFR. It just falls on its face after squirters are done. I have 13.5 at idle and 14.2 at 60 (3K RPM) cruising. Checked for vacuum leaks with carb cleaner even replaced throttle plate bushing front and back little more slop than I liked in them (thinking air leak). Transition slots are squared primary and secondary when closed. 4 corner idle (1 3/4 turns out) 82 primary main and 84 secondary main jets, 37 main Squirter and 35 secondary . I have 14 degrees base timing and 18 on Mechanical ( Lt blue and Lt silver springs in MSD distributor) for a total of 32 degrees total by 3000 RPM. Whats your thoughts, Thanks in advance.
i had same issue with my QFT SQ 750 which is a double pumper on my Chevy 462 lean cruise at around 1500 rpm.. checked for vac leaks, timing , float level .. i them opened the Idle restrictor jets on the metering block as shown in this vid from about .029" to .035 and it fixed the problem !
So I’m struggling with the pop Pop Pop misfire at light partial throttle and I’m glad I found this video. I’m going to either drill open 2 sizes or try to tap that for some kind of replaceable jet. Thanks for explaining this clearly .
Thanks! We just went through this tunning my friends carb. We went from a 28 to a 32 on the IFR and increased the main jets from a 65 to a 69 and it made a HUGE difference. His main circuit is a little lean still so we will increase the jet 2 more sizes but the IFRs are right on.
@@frankdatank7751 Thats actually not a good idea because if its a stock mechanical distributor, its going to advance the timing curve way too far out and could cause spark knock. A safe zone is right around 13-15 at idle and 32-36 all in on regular pump gas. The vacuum advance can give you a little more breathing room but you do gotta be careful not to go too far
I have a holley brawler 600 vac secondary on an Lt1 with stock cam, intake and headers. When i am off throttle its pulling 25hg vacuum and pops and farts until i knock it out of gear (manual). My 02 goes lean to 18/1 and even though its not under load its annoying. It idles fine (19hg), ive adjusted it a bit rich, it cruises fine 13/14/1, if i stomp on the gas i get a good shot of fuel, no pops or bogging. Every other circuit is fine. If say i sit in neutral and gently raise rpm and hold it at say 1500 it goes lean. Ive tried silly big jets, adjusting idle screws all sorts. I just cant stop this transitionary lean spot, but only not under load, under load its fine. I havent tried adjusting the secondary idle position to maybe expose the secondary idle slot a bit more, but other than that i'm stuck. My timing is a good 15degree base timing, altho it is possible its not advancing enough as im using an msd with springs so obviously different curves.
Off idle, high vacuum, lean is normal since the engine is basically engine braking when you let off the throttle. A lot of the time, the popping comes from an exhaust leak that mixes with the unburned fuel. In factory carbureted cars, they had a little dashpot that would slow down the idle closing so it wouldnt pop. A lean idle mixture or too far open idle speed screw will also cause that. On some cars, I just keep the throttle a hair open as I slow down and it doesnt pop.
If u are pulling vacuum through the ported vacuum that's the same as the manifold vacuum is that a good indication your transfer slots are too far open.
@@NightWrencher I just put a Holley brawler on my 350 Chevy and the cam is way too big for a out of the box carb so I'm going to be doing some modifications. Would u suggest drilling holes or opening the secondary throttle with the set screw. I'm experiencing everything u described off idle bog surging at under 2500 rpm all related to transfer slots being too exposed. With mechanical secondary and 4 corner idle mixture maybe drilling holes is the way to go.
@@NightWrencher maybe my carb is defective out of the box I slid a piece of paper under the secondary set screw to increase the idle to about 900 rpm with the primary transfer set screw backed all the way out so they should be pretty much closed and I'm still getting manifold vacuum at my ported spot instead of only off idle.
Finally found someone smart enough to talk about the right issue. I swear if one more person say ignition to my im going to loosen their teeth. To it, im having the EXACT issue youre talking about, ive bodged it together by richening the main circuit. Heres where i get confused, warmed up, put new plugs in, drove 20 miles very gently, ie, keeping power valve closed. Plugs are black.. go any leaner in the mains and it wont even hold 55 without popping and bucking. Soon as power valve opens, runs perfect. Even free rev is pretty trashy until 2800ish then it smoothes right out perfect. How is it so rich and running like its so lean... 71 idle air bleeds, 70 primary jet, qft 680 hr vs on a 231@.050 cammed 351
Did you check your ignition? Lol just kidding. Sounds like a typical IFR too small condition. Theres very little info on specific circuit sizes on aftermarket carbs so without a pin gauge set or wideband o2 gauge, you're probably going to be just guessing. Most mild builds Ive seen like a .032 in the IFRs. You can go to your local small town hardware store and ask for a .032 or #67 drill bit and open up your IFRs. This is permanent so I suggest getting a wideband before doing some serious mods to your carb. A wideband litterally pays for itself within the first month. Lets you pull out several MPG from perfectly adjusting your tune.
Heres another thing to think about. It could be that your IFRs are too big already since its a QFT 680 but your main jets are too lean. In which case your light throttle cruise would be rich but your throttle from 1/4 into right before the power valve would be lean until the PV open which puts it back in the rich zone. Like I said you need a few more tools to be able to dial it in bit once you got it, youll be golden
@@NightWrencher Just now seen these, but here we go. Finally got my wideband back, though not installed yet. I have removable IFR's, they were blanks that were drilled by my carb builder. Using some .030" welding wire as a gauge i would guess they were around .033". The only bit i had even close was .0365" so i used it. Right or wrong i decided to test two theories at once and also changed to 65s in the primary. Everything is much improved, idle quality, vacuum, response etc. Popping and bucking is virtually gone. I do have a hint of a flat spot at tip now, basically unnoticeable (may need less pump shot now). There is also a little bit of a flat from either transition to main, or secondary opening. Wasnt able to drive much to get it figured. That said, overall experience vastly improved, throttle response and torque under the cam is a big improvement, it went from blowing the tires off at ease to, oops, didnt mean to do that. Thanks for the handy AF video friend. Ironically, did also find that my brand new Ford motorsport 8.5mm super conductor coil wire was in fact leaking, that was the last thing i fixed.
@@doxnoogle5782 I'm glad it worked out! Carb issues are a pain when you dont know where to look. Looks like you might need more pump shot now though but I'd wait until you install the wideband before continuing the tuning process
Hey thanks 👍 what about if your cracking the rear vacuum secondary open to raise the idle slightly.? the rear metering block has IFR as well some say that's a square style set up and to open secondary transfer slots just like the front or should they be completely closed ?
It should only be opened IF you have a 4 corner idle carburetor. If you open them on a 2 corner idle carb, you'll run lean at part throttle as if you had a vacuum leak.
@@NightWrencher i just received a micro mark drill bit set it goes from size# 61 to#80. I have 2 metering blocks 1 is for a 600 has the IFR incerts on the bottom and 1 for a 670 new block the IFR incerts on top the incerts on both are way over 61 size 0.39 I'm not sure what size they are but maybe in the 45 + size do they come like that ? My 600 block is # 10884 -3 the 670 # is 11761 -1
I was thinking of buying the adjustable metering block from pro-form standard calibration they have the drilled IFR and pV with 3 emulsion each side . The other choice was the Quick fuel one pretty much same thing or AED .
The proforms come with a pretty good calibration from the factory so thats a good option. If the blocks are unmolested, check inside the insert and make sure theres not a smaller hole inside of the insert itself. Factory usually has them somewhere between .028-.036
The stock blocks on them have a lot of meat to drill them out and put in plugs. If you dont want to mess with it, there are plenty of aftermarket blocks available. Stick with more well known company blocks like AED, quickfuel, proform, pro systems etc. They have better metering. I have a no name block and theres an issue where Itll bypass the idle circuit and just dump fuel even if theyre fully closed.
@@jakefriesenjake they'll fit, its a standard holley pattern. The only thing that maybe prevent it from bolting on is that sometimes the pegs are too long and you need to trim them. Other than that, youre fine.
@@NightWrencher yeah, sounds right.... The guys didn't sound to knowledgeable.... On the Proform site, in the instructions download, it says that the one fits all demons.... So I just bought set screws and drills and taps in sizes 6-32, 8-32, and 10-32
So ... should I take off my carb to set those butterfly just right or should I just back off idle screw until it barely touch and that should be just right for transition?.
For setting up the idle the first time I like to start at 2 full turns in so that the carburetor idles around 1500-2000 and then start working it down. Once you set the idle, you can back the idle screw all the way out to see how much adjustment was left. I'm usually about a half turn in.
My 355 when setup at idle my primaries are open maybe. 025". It gives that popping and shake about 2000 rpm cruise. It's a 236/242 .050 duration cam with 5" of vacuum at idle. Should I drill my transition restrictor or open the secondaries just a tad. Idles and starts good. It cranks more when it's hot before it starts, but still starts. I think it's because there isn't enough signal going through the idle circuit because the primaries are open just slightly. Idle is 800-850 rpm.
Long starts when hot usually means rich but if theres no issues, I wouldnt worry about it. The issue with the cruise popping would probably be fixed by opening up the IFRs. I wouldnt try to open up the secondaries unless 1) you have open the primaries too much to get it to idle and 2) its a 4 corner idle carb. Figure out where your carb is at before you start drilling but most carbs Ive seen are happy with a .032 or .034 size on the IFRs. Good luck
@@NightWrencher it's a 750cfm AED (Holley) mechanical secondaries. I had it off today and found that the secondaries were slightly sticking in the bores. I adjusted the stop screw 1/3 of a turn after contact with the linkage. This has little to no effect on idle. I'll try drilling the restrictor when I get my hands on some of those tiny drills. My set only goes down to. 040". It's hard to measure the gap on the primaries with feeler gauges, so I'm guessing at the distance, but somewhere between .020 and .025"
I have the same carb as yours on my plymouth gtx..but my engine dies whenever i put in gears R or D. I already clean and overhaul the carburator but stiil got the same issue..can you help me sir?i will appreciate much, thanks you sir..
Have a Holley marine carb that when idling fuel drips out of the primary venturi booster. Check float level, needle valve seat, power valve, and transition slot exposure. Everything seems fine and running 16" vacuum when idling. Was going to check fuel line pressure (mechanical fuel pump). Any other thoughts. Appreciate it!
I would definitely check fuel pressure and double check your float height. Also make sure that your air bleeds are not clogged because that will also make the fuel pull but typically it's a fuel level issue make sure you don't have more than 6 PSI and go from there
On cold start Holley 750 vac secondary is super rich that causes miss. Fire gets only slightly better as it warms this is a new carburetor best vacuum is 12 any ideas
Ok, I just gotta ask all the basic questions because some people dont check. Have you tried resetting the idle from scratch? I have a video on it if you havnt seen it
@@NightWrencher going to pull carb and recheck everything mixture screws have little effect cam is 528 intake 536 exhaust, the duration is 221 intake/226 exhaust @.050- 110degrees lobe separation. 10.0:1 compression if this helps
Actually tons of problems come from misadjusted transfer slot and too small IFRs. Its easy to see on an AFR gauge but hard to pinpoint by ear where the problems are at
Thats an interesting idea but you can basically eyeball where youre at depending on how many turns you got on the throttle stop. Shouldnt be more than one turm on a stock engine with good timing at idle
My carb won't idle at all. 350 CI SBC with mild performance Lunati cam. Carb is a 650 double pumper with 4 idle circuits. After fixing two leaks, (front Accelerator pump housing and stripped rear bowl screw), it would not idle and just died unless I opened the throttle plates a lot. Also my idle vacuum that was 19 in hg at 750 rpm is now 15 in hg. I had to ask myself what did I change? All new gaskets, new needle cork seals, new needle and seats. But, I later remembered that I had put some silicon grease on the needles and seals to help them go in. That's the only thing different from a normal rebuild, that I did. I now honestly think that the silicon grease and non ethanol gas plus octane booster I run, somehow formed some chunks or goo that clogged the idle restrictors in the metering blocks. So I did a super clean out of all passages but that still didn't fix the problem. I can adjust the screws in to the stops but it still runs, but rough. Probably because it's running on the transfer slots since the idle stop is so far open. I ordered new metering blocks yesterday and will find out if that is the problem. I hope it is because I'm running out of ideas. Great informational video, thank you.
Your engine is supposed to die when you turn in the idle screws all the way in. To me it sounds like an internal leak and its running super rich. I would check 2 things, first, make sure you used the right gasket for the metering block, there are 2 styles, 1 with the hole for the accel pump shot and another with the same hole but its part of the hole for the power valve. Ill upload a picture on my instagram to illustrate what I mean. The second thing I would check is your float height. If its too high or your fuel pressure is a little too high, itll start pouring down the boosters. While its idling carefully look inside the thoats and make sure the boosters arnt leaking. Check those 2 things and lmk. Ill upload a pic on my instagram right now.
@@NightWrencher I closely matched the new blue gaskets to my old black ones. All holes are exactly the same. It's acting like there is zero fuel going to the idle circuits/needles. Starts okay, then idles down and dies. I opened the needles up to 2 full turns out and same thing, until I adjust the throttle stop open and expose the transfer slots. Then it does idle but not like it always used to and the vacuum is 4" lower. There's no fuel dripping from the boosters and it revs great just like before. It never did this before I put that damn silicon grease on the needles and cork seals. I get my new metering blocks in a week and I'll see what they do. Hoping for the best. Thanks for the reply.
Your vacuum doesnt have too much to do with your issue, itll resolve itself when the carb runs correctly. If you pour gas down the throat will it idle for a bit then die or does it make it worse? Also, did you replace the gasket for the baseplate? Some of them are almost exactly the same but the 2 holes on each corner of the main body that feed the transfer slot are offset and will block fuel from being fed into the transfer slot. Also make sure your big vacuum lines for the booster/pcv are plugged while you diagnose your issue. If your passage for the needle and seat are clear, it would be wise to blow out all the passages in the main body just to make sure none of them are plugged. It sounds like the issues are for both front and back so do make sure the baseplate gasket lines up perfectly with all the main body holes
@@NightWrencher By baseplate gasket you are talking about the one between the body and the throttle plate? I did change that and I'll compare it to the old one that was in there. The transfer slots seem to be getting fuel but the idle holes aren't. Sure will be nice to get it running clean and stable like before I rebuilt it. I did blow out the main body holes with 60 psi air. Got some gas in the face and they seem ok. The low vacuum is an indicator that there's not enough fuel at idle. That should come back with the new metering plates and the throttle plate adjusted back to covering almost all of the transitions slots. Thanks for all the replies. I'll let you know what happens.
If I might Add, it is almost as likely that the IFR's are too large, and the flat level steady cruise easy tip-in has a stumble, and the afr gauge shows a 11:1, Then test putting a .01x" diameter piece of wire in both front IFR's and do a test drive. Point is, some stumbles are RICH stumbles from intermittent over fueling. Not all stumbles are lean stumbles, are they? Insult to injury, increasing pump shot in an attempt to remedy an over-rich top-of-transfer-slot, pre-main booster, steady state condition gently transitioning faster, no?
Cool, im glad i found this. Been tuning on my 80 malibu, 383 with a QF670, ive got everything pretty good but at very light throttle, it hesitates and spikes lean to around 16:1. Ive messed with the transfer slot, ive messed with the ifr's. Pretty sure its the transfer slot adj as they are around 60 thousandths. I thought it was due to me dropping to a 30 ifr, but it did it too with a 35 ifr, tells me its the transfer slot.
The transfer slot is non adjustible, only the opening is adjustible which you should have as closed as possible. When it hesitates and spikes, the number you see isnt the exact number since the misfire causes the hesitation which increases the o2 in the exhaust and makes it read leaner than it is. You need to tune based on consistancies so keep the throttle steady in high gear in the transition and read the AFR. If it constantly reads lean, you need bigger IFRs. If your RPMs are too low and the engine is bogging, thatll cause hesistation as well. A lot of things to consider. When I tuned a holley 670 for a 383 last year we ended on a 32 ifr and 70 primary jets. And 50cc accelerator pump with 13 degrees initial timing and 36 total. Good luck
@@NightWrencher It has had this lean spike no matter what adjustment i do, i checked the transfer slot and it was around 60 thousandths. it idles at 13.8, cruise is 13.2-13.5, and power is 12.5. The only time it has the lean spike is very light throttle, like cruising thru a parking lot, when ya let off then ease back into it, it spikes to 16 and hesitates.. its not the acc pump either cause thats on point. anyways thanks for the reply
I have Holley that was rebuilt by the guy that rebuilt my 68 cougar 390 motor, close to stock rebuilt. Engine was dyno on engine stand and broken in. Installed engine, over a year ago, and can not get the car to stop hesitation off the line. Engine guy broke vacuum advance and had a Pertronix 2 ignition system in car. I have tried a lot of things, new distributor Pertronix 3 with vacuum advance, now i have gone back to stock distributor with points and stock coil, I still had the hesitation. We noticed that with a timing light on the coil wire, and vacuum advance hooked up, the light goes out for and instant during acceleration, when vacuum is disconnected, when we give it gas, timing light does not cut out. I have tried another 600 carb, same results. I have tried set the carb, ideal screws, transfer slot, (not sure if the rear plates are correct), now I can not get the car to go in gear, it idles. Not sure what I did or how to fix this car
Thank you I am going to try agin this weekend to see if I can see anything else wrong on the carb. Ai also noticed that there is a little gas coming out of i Guess a seal on the side where the throttle arm attaches to the butterfly. Not sure if my kit comes with this seal or if it is possible or mr to replace it
I also have a very small a little bigger than a pin, below my transaction slot, all the outer carbs I have seen have bigger holes, is this where the idle circuit adds fuel to the car. I can send you a picture
@@marionazareth6417 Hi Mario, it sounds like you actually have a reverse idle setup. so that means that your baseplate has that pin hole (same diameter as the slot approx. .030) below the transfer slot- the small hole is the curb idle discharge, and both that AND the slot are served by the same circuit. AND, your mixture screws work in reverse- they actually meter additional air via a 2nd air bleed on the primary bores of the main body underneath the main boosters. so, clockwise adjustment richens, and counterclockwise adjustment leans the curb idle mixture. flip your carb over, open the primary throttle and look to see if you have these extra holes, they are slightly smaller than 1/8 inch diameter. I can explain more off line and I have photos of my carb parts that also are reverse idle
Thanks for the video. Very informative. Should the secondary transfer be set the same way with a little square showing in the transfer slot? Also, could a bad throttle cable setting cause a rich situation? Seems like the idle mixture screws are making no difference and it runs real rich.
Hey, if you have a 4 corner idle carb, you should square up the rear transfer slot and then set the front. If you have a problem with the idle being too rich, run the screws all the way down until they bottom out while the car is running and it should kill the car. If it does not kill it completely you have an internal fuel leak either from the float being too high or having a blown power valve. Check that and get back to me and let me know what you find
Sorry bud but I don’t know what a 4 corner idle is? I checked the power valve. It looks fine and it is brand new. I also can bottom out both idle screws and the engine does not cut off.
Well then I think we found your problem. If you only have 2 idle screws in the front, its a 2 corner idle. If it also has 2 in the back, its a 4 corner idle. Did you check your float levels? While running, they should just bearly be dripping out of the sight hole. If you take the sight plug off, only a little bit of fuel should come out. If its pouring out, your floats are too high
It it’s a marine Holley. It doesn’t have site holes or the ability to adjust the float level like that car ones. I checked them when I had them out and they looked level when they were shut. Thank you for your patience BTW
Sometimes it's the power valve causing an off idle stumble is the power valve is too. If you have a lot of vaccum and a low level power valve you can go up from a 6.5 to a 8.5 and fix the problem.
Actually the PV circuit has nothing to do with an off idle stumble. If you are able to go into the PV circuit off idle then youll be going into it alongside the main jets which also has nothing to do which off idle performance. Fuel from the PV and main jets comes out of the boosters but when you're coming off idle, the throttle plates arnt open far enough to pull vacuum off the boosters and even if it did, fuel would take too long to travel through the entire circuit to make any difference off idle. Off idle performance is dictated by idle screws, transfer slot, IFRs, accel pump cam and accel pump nozzle. Thats it.
@@NightWrencher So you trying to tell me, a ASC Certified Master tech for the last 40 years who has had and raced cars with Holley carbs on all of my street cars and drag cars I don't know what I am talking about?
@@kennywhiddon1497 yeah, basically. Racing a holley and daily driving a holley are 2 different things. You tend to ignore too many things when you can sit on the trans brake at part throttle. If your idle vacuum is at say 18 and you have an 8.5pv installed, you would have to go pretty deep into the pedal or drive a heavy car with tall gears to get your vacuum down far enough for it to open long enough to make any difference. I drive with a vacuum/boost gauge so I see the numbers all day long. My idle vacuum in my LS is 22hg. Driving a stick, with 35 tires on 3.73 gears, the lowest vacuum I see off a stop light is 12hg unloaded and only see 5-0hg when pulling a trailer. The PV circuit just does not respond fast enough to make any difference off idle and I invite you to show me any holley books or articles written by experts to prove me wrong. If I'm wrong, I'm wrong, but there's gotta be evidence.
@@NightWrencher I have fixed more drivability problems with Holley carbs on street cars in the last 40 years than you could ever imagine, not all problems are found in books, people mismatch jets, power valves and improperly set ignition timing and advance curves all the time as well as have the wrong heat range spark plugs. Every thing must work together. By the way, if you are on the trans. brake at part throttle, you must have never heard of a two step. Most off idle stumbles are on cars and trucks with a automatic trans.
Ok but thats not what we are talking about. We are not talking about mismatched parts, incorrectly installed parts or messed up timing. We are talking about the fundamentals of a specific system. We are talking about instantaneous off idle performance. You are stopped, you attempt to go, stumbles, then picks up. A power valve will not cure that. Maybe more timing, maybe wider plug gaps, maybe a bigger pump shot, but thats not what a power valve is for. A power valve adds fuel to the primary circuit. If the boosters arn't flowing fuel, the PV isn't contributing. I can see what you are trying to say, but thats not off idle performance.
Would be nice if they would of had 2 needles, side by side. One for the idle mix (normal), and another on top of it (to set the flow of the transfer slots). I know that it's more stuff to mess with and get wrong, but oh well
If you drill the idle feed too big, grab a small piece of stranded wire and bend it over in the hole. When you put the gasket on it will hold the wire in place. (An old Holley trick)
Soy boliviano pido por favor explicación en español tengo el problema del afinado y no puedo haser q funcione en ralenti por fa un número para llamada directa quedaré muy agradecido
Motorcycle carb work slightly different. Lol lots of timers run there car to rich n don't even check there timing. Fyi my Motorcycles don't smelled like gas when i twist the trottle.
Dude you are the man. Giving the most in depth explain actions of Holley carbs of ANY video I’ve ever watched trying to understand them. I recently did a 5.0 swap on an 88 Ford ranger using a 302 out in an 89 fox body, converted from EFI to Holley street warrior 600 just because I wanted old school simplicity of no sensors to worry about. Turns out tuning the carb to run the way it should isn’t so simple if you don’t understand them. I was just about to pay a guy to tune it for me until I found your videos, now I’m highly considering doing it myself!
Thanks man, trust me when I say most of those carb "tuners" only understand the basics. They will set your timing, idle and maybe jetting but thats where it ends. A drivability tune takes a lot of time to get 100% and no 2 cars are the same. You'll get frustrated, but by the time you're done, theres nothing better.
@@NightWrencher one question I have is about vacuume secondaries. I don’t think mine are opening even with the lightest spring in the diaphragm. Could that be due to jet/power valve tuning or is it simply because it’s running with a manual transmission? I’ve read that vacuume secondary is best suited for an automatic trans because the motor is under more of a load to generate more vacuume but I figure if I’m stomping on the gas in 2nd-3rd gear those secondaries should be engaging.
It don’t take much to get the truck moving, big HP to weight ratio, but it should have more pickup in the higher gears than it has IMO. Acts like it’s still running on 2 barrels when I stab it in the higher gears starting from about 2k RPMS
Have you tried the paper clip trick to see if they are actually opening? regardless of engine size, the secondaries should open once the throttle is opened far enough.
hell yeah, this is exactly what i needed. this is the only video ive been able to find on this.
The Metering Block Idle Feed Restriction and the Main Body Idle Air Bleed make an emulsion that feeds both the round Curb Idle Discharge Hole AND the Transfer Slot... The Idle Mixture Screw adjust the amount of Idle Emulsion delivered out of the round curb idle discharge hole. The Transfer Slot is fed from the same Idle Well, BUT the Transfer Slot Feed is UPSTREAM of the Idle Mixture Screw, so it 'robs' all the emulsion from the round Curb Idle discharge hole IF the Transfer Slot is over exposed and control of the idle mixture discharge from the round curb idle discharge hole by way of the mixture Screw is lost IF the Transfer Slot is over exposed. Does that make sense?
Excellent explaination. This is probably the least understood and most cruical circuit for a street car.
I just replied to Nightwrencher;
"My carb won't idle at all. 350 CI SBC with mild performance Lunati cam. Carb is a 650 double pumper with 4 idle circuits. After fixing two leaks, (front Accelerator pump housing and stripped rear bowl screw), it would not idle and just died unless I opened the throttle plates a lot. Also my idle vacuum that was 19 in hg at 750 rpm is now 15 in hg. I had to ask myself what did I change? All new gaskets, new needle cork seals, new needle and seats. But, I later remembered that I had put some silicon grease on the needles and seals to help them go in. That's the only thing different from a normal rebuild, that I did. I now honestly think that the silicon grease and non ethanol gas plus octane booster I run, somehow formed some chunks or goo that clogged the idle restrictors in the metering blocks. So I did a super clean out of all passages but that still didn't fix the problem. I can adjust the screws in to the stops but it still runs, but rough. Probably because it's running on the transfer slots since the idle stop is so far open. I ordered new metering blocks yesterday and will find out if that is the problem. I hope it is because I'm running out of ideas. Great informational video, thank you."
Olsketchmo; Your explanation of the idle circuit and transfer slots is really great information. I thought I knew a lot about Holleys, now I know more. Thank you.
@@novakenss please post results of new metering blocks. Thanks.
Why is definitely important: control of idle mixture fades the more slot is exposed - they compete from the same fuel well in the metering block, and... transfer slot is closer to the source. When throttle opens to expose all the transfer slot, the idle mixture screw port sees a nearly equalized signal on either side and idle port flow suffers. You did the right thing tuning by vacuum: it reveals the quality of tune like clockwork.
Thanks for an excellent explanation of properly setting up the Idle and Transition circuit on a Holley. I like it that you have mentioned some of the problems of the circuits and what they do as well as how to fix them in a procedural way.
Thank you! I appreciate it!
@@NightWrencher good stuff.
You did miss one very important thing with more high performance/race type engines.
Throttle blade air bypass hole.
Basically similar thing, hot w/ idle/air... close
Just keep drilling the bypass holes in all throttle blades until it idles in the neighborhood of where you want it to.
Race engines with bigger cams wont idle w/o that and people go cranking on that idle screw, get into the transfer slot and have a mad hesitation, try and crutch...
Fairly simple thing. Once you know where you need to be, you can order throttle blades with the right size hole when you set out to build a carb for a similar application.
The Holley Ultra XP has a different bypass by the air cleaner stud, but not everyone runs that.
More than okay with no videos covering this 😅🤫
Thanks for the video. It helped me figure out that I needed vacuum on the metering block.
Glad I could help!
Thank you so much man!
Your video help me understand what I was doing wrong trying to set my idle.
Thank you! Did you get it set up?
thanks for explaining this, it sounds exactly like what my 468 with the 670 Brawler is doing now i have an idea where to be looking..
Awesome, I hope it works out!
Yess this is right had the same problem with my hp ultra ifr was to small
Where did you get that aftermarket metering block from? Your content and explanation of things is on point in all of your videos I've seen, thank you!
I got a bunch of them from a guy out in Kentuckey. HPR Carbs, his name is Johnathan. Sells all kinds of new and used holley parts at a good price. Look him up on facebook
I have a Holley Speed Demon 750DP carb that I can't get to drive at low speeds about 20 or 25MPH cruising the neighborhood it goes lean about 20 + AFR. It just falls on its face after squirters are done. I have 13.5 at idle and 14.2 at 60 (3K RPM) cruising. Checked for vacuum leaks with carb cleaner even replaced throttle plate bushing front and back little more slop than I liked in them (thinking air leak). Transition slots are squared primary and secondary when closed. 4 corner idle (1 3/4 turns out) 82 primary main and 84 secondary main jets, 37 main Squirter and 35 secondary . I have 14 degrees base timing and 18 on Mechanical ( Lt blue and Lt silver springs in MSD distributor) for a total of 32 degrees total by 3000 RPM. Whats your thoughts, Thanks in advance.
How large are your IFRs?
@@NightWrencher I wish I knew. They are inserts and non adjustable. I only have a pin gauge set that goes up to .060 need a bigger set I guess.
i had same issue with my QFT SQ 750 which is a double pumper on my Chevy 462 lean cruise at around 1500 rpm.. checked for vac leaks, timing , float level .. i them opened the Idle restrictor jets on the metering block as shown in this vid from about .029" to .035 and it fixed the problem !
So I’m struggling with the pop
Pop
Pop misfire at light partial throttle and I’m glad I found this video.
I’m going to either drill open 2 sizes or try to tap that for some kind of replaceable jet.
Thanks for explaining this clearly .
Thanks! We just went through this tunning my friends carb. We went from a 28 to a 32 on the IFR and increased the main jets from a 65 to a 69 and it made a HUGE difference. His main circuit is a little lean still so we will increase the jet 2 more sizes but the IFRs are right on.
Popping is going to be your timing,
Add more timing 20-25 idle or off idle.
@@frankdatank7751 Thats actually not a good idea because if its a stock mechanical distributor, its going to advance the timing curve way too far out and could cause spark knock. A safe zone is right around 13-15 at idle and 32-36 all in on regular pump gas. The vacuum advance can give you a little more breathing room but you do gotta be careful not to go too far
Fatten it up
if you compare the idle feed restrictors to the idle air bleeds, which would one would have a bigger effect on the transition?
I have a holley brawler 600 vac secondary on an Lt1 with stock cam, intake and headers. When i am off throttle its pulling 25hg vacuum and pops and farts until i knock it out of gear (manual). My 02 goes lean to 18/1 and even though its not under load its annoying. It idles fine (19hg), ive adjusted it a bit rich, it cruises fine 13/14/1, if i stomp on the gas i get a good shot of fuel, no pops or bogging. Every other circuit is fine. If say i sit in neutral and gently raise rpm and hold it at say 1500 it goes lean. Ive tried silly big jets, adjusting idle screws all sorts. I just cant stop this transitionary lean spot, but only not under load, under load its fine. I havent tried adjusting the secondary idle position to maybe expose the secondary idle slot a bit more, but other than that i'm stuck. My timing is a good 15degree base timing, altho it is possible its not advancing enough as im using an msd with springs so obviously different curves.
Off idle, high vacuum, lean is normal since the engine is basically engine braking when you let off the throttle. A lot of the time, the popping comes from an exhaust leak that mixes with the unburned fuel. In factory carbureted cars, they had a little dashpot that would slow down the idle closing so it wouldnt pop. A lean idle mixture or too far open idle speed screw will also cause that. On some cars, I just keep the throttle a hair open as I slow down and it doesnt pop.
Great vid my friend !!! This totally helped me out !!!
Thats awesome! I'm glad to hear it!
Great commentary! Very difficult to stop laughing after I saw the fist face eating the screwdriver at 0:24 !!!
🤣 I told you to ignore it!
Okey ill try..ill let you know if that helps..thank you sir.
If u are pulling vacuum through the ported vacuum that's the same as the manifold vacuum is that a good indication your transfer slots are too far open.
Yes exactly
@@NightWrencher I just put a Holley brawler on my 350 Chevy and the cam is way too big for a out of the box carb so I'm going to be doing some modifications. Would u suggest drilling holes or opening the secondary throttle with the set screw. I'm experiencing everything u described off idle bog surging at under 2500 rpm all related to transfer slots being too exposed. With mechanical secondary and 4 corner idle mixture maybe drilling holes is the way to go.
If you've got a 4 corner idle carb, opening the secondaries would be the best way to go 👍
@@NightWrencher maybe my carb is defective out of the box I slid a piece of paper under the secondary set screw to increase the idle to about 900 rpm with the primary transfer set screw backed all the way out so they should be pretty much closed and I'm still getting manifold vacuum at my ported spot instead of only off idle.
Are you sure thats the ported vacuum port?
Finally found someone smart enough to talk about the right issue. I swear if one more person say ignition to my im going to loosen their teeth.
To it, im having the EXACT issue youre talking about, ive bodged it together by richening the main circuit. Heres where i get confused, warmed up, put new plugs in, drove 20 miles very gently, ie, keeping power valve closed. Plugs are black.. go any leaner in the mains and it wont even hold 55 without popping and bucking. Soon as power valve opens, runs perfect. Even free rev is pretty trashy until 2800ish then it smoothes right out perfect. How is it so rich and running like its so lean... 71 idle air bleeds, 70 primary jet, qft 680 hr vs on a 231@.050 cammed 351
Did you check your ignition? Lol just kidding. Sounds like a typical IFR too small condition. Theres very little info on specific circuit sizes on aftermarket carbs so without a pin gauge set or wideband o2 gauge, you're probably going to be just guessing. Most mild builds Ive seen like a .032 in the IFRs. You can go to your local small town hardware store and ask for a .032 or #67 drill bit and open up your IFRs. This is permanent so I suggest getting a wideband before doing some serious mods to your carb. A wideband litterally pays for itself within the first month. Lets you pull out several MPG from perfectly adjusting your tune.
Heres another thing to think about. It could be that your IFRs are too big already since its a QFT 680 but your main jets are too lean. In which case your light throttle cruise would be rich but your throttle from 1/4 into right before the power valve would be lean until the PV open which puts it back in the rich zone. Like I said you need a few more tools to be able to dial it in bit once you got it, youll be golden
@@NightWrencher Just now seen these, but here we go. Finally got my wideband back, though not installed yet. I have removable IFR's, they were blanks that were drilled by my carb builder. Using some .030" welding wire as a gauge i would guess they were around .033". The only bit i had even close was .0365" so i used it. Right or wrong i decided to test two theories at once and also changed to 65s in the primary. Everything is much improved, idle quality, vacuum, response etc. Popping and bucking is virtually gone. I do have a hint of a flat spot at tip now, basically unnoticeable (may need less pump shot now). There is also a little bit of a flat from either transition to main, or secondary opening. Wasnt able to drive much to get it figured. That said, overall experience vastly improved, throttle response and torque under the cam is a big improvement, it went from blowing the tires off at ease to, oops, didnt mean to do that. Thanks for the handy AF video friend. Ironically, did also find that my brand new Ford motorsport 8.5mm super conductor coil wire was in fact leaking, that was the last thing i fixed.
@@doxnoogle5782 I'm glad it worked out! Carb issues are a pain when you dont know where to look. Looks like you might need more pump shot now though but I'd wait until you install the wideband before continuing the tuning process
Hey thanks 👍 what about if your cracking the rear vacuum secondary open to raise the idle slightly.? the rear metering block has IFR as well some say that's a square style set up and to open secondary transfer slots just like the front or should they be completely closed ?
It should only be opened IF you have a 4 corner idle carburetor. If you open them on a 2 corner idle carb, you'll run lean at part throttle as if you had a vacuum leak.
@@NightWrencher got it thanks
@@NightWrencher i just received a micro mark drill bit set it goes from size# 61 to#80.
I have 2 metering blocks 1 is for a 600 has the IFR incerts on the bottom and 1 for a 670 new block the IFR incerts on top the incerts on both are way over 61 size 0.39 I'm not sure what size they are but maybe in the 45 + size do they come like that ? My 600 block is # 10884 -3 the 670 # is 11761 -1
I was thinking of buying the adjustable metering block from pro-form standard calibration they have the drilled IFR and pV with 3 emulsion each side . The other choice was the Quick fuel one pretty much same thing or AED .
The proforms come with a pretty good calibration from the factory so thats a good option. If the blocks are unmolested, check inside the insert and make sure theres not a smaller hole inside of the insert itself. Factory usually has them somewhere between .028-.036
Awesome video.
Do you know of a billet block that will fill or a old school speed demon Barry Grant carb? I want/need more adjustments
The stock blocks on them have a lot of meat to drill them out and put in plugs. If you dont want to mess with it, there are plenty of aftermarket blocks available. Stick with more well known company blocks like AED, quickfuel, proform, pro systems etc. They have better metering. I have a no name block and theres an issue where Itll bypass the idle circuit and just dump fuel even if theyre fully closed.
@@NightWrencher I called Proform and aed, they can't confirm that they will fit......
@@jakefriesenjake they'll fit, its a standard holley pattern. The only thing that maybe prevent it from bolting on is that sometimes the pegs are too long and you need to trim them. Other than that, youre fine.
@@NightWrencher yeah, sounds right.... The guys didn't sound to knowledgeable.... On the Proform site, in the instructions download, it says that the one fits all demons.... So I just bought set screws and drills and taps in sizes 6-32, 8-32, and 10-32
Nice, so youre sticking with the stock block?
So ... should I take off my carb to set those butterfly just right or should I just back off idle screw until it barely touch and that should be just right for transition?.
For setting up the idle the first time I like to start at 2 full turns in so that the carburetor idles around 1500-2000 and then start working it down. Once you set the idle, you can back the idle screw all the way out to see how much adjustment was left. I'm usually about a half turn in.
My 355 when setup at idle my primaries are open maybe. 025". It gives that popping and shake about 2000 rpm cruise. It's a 236/242 .050 duration cam with 5" of vacuum at idle. Should I drill my transition restrictor or open the secondaries just a tad. Idles and starts good. It cranks more when it's hot before it starts, but still starts. I think it's because there isn't enough signal going through the idle circuit because the primaries are open just slightly. Idle is 800-850 rpm.
Long starts when hot usually means rich but if theres no issues, I wouldnt worry about it. The issue with the cruise popping would probably be fixed by opening up the IFRs. I wouldnt try to open up the secondaries unless 1) you have open the primaries too much to get it to idle and 2) its a 4 corner idle carb. Figure out where your carb is at before you start drilling but most carbs Ive seen are happy with a .032 or .034 size on the IFRs. Good luck
@@NightWrencher it's a 750cfm AED (Holley) mechanical secondaries. I had it off today and found that the secondaries were slightly sticking in the bores. I adjusted the stop screw 1/3 of a turn after contact with the linkage. This has little to no effect on idle. I'll try drilling the restrictor when I get my hands on some of those tiny drills. My set only goes down to. 040". It's hard to measure the gap on the primaries with feeler gauges, so I'm guessing at the distance, but somewhere between .020 and .025"
You dont really need to measure the gap in the t slot, just get it as closed as you can while mainting a good idle
I have the same carb as yours on my plymouth gtx..but my engine dies whenever i put in gears R or D. I already clean and overhaul the carburator but stiil got the same issue..can you help me sir?i will appreciate much, thanks you sir..
Chances are that your car idle is too lean or your ifrs are too small. Try turning out the idle screw a quarter turn each and see if that helps
Okey ill try..ill let you know if thats helps..thank you sir..
Have a Holley marine carb that when idling fuel drips out of the primary venturi booster. Check float level, needle valve seat, power valve, and transition slot exposure. Everything seems fine and running 16" vacuum when idling. Was going to check fuel line pressure (mechanical fuel pump). Any other thoughts. Appreciate it!
I would definitely check fuel pressure and double check your float height. Also make sure that your air bleeds are not clogged because that will also make the fuel pull but typically it's a fuel level issue make sure you don't have more than 6 PSI and go from there
@@NightWrencher Thank you very much. I will let you know after I check it!
On cold start Holley 750 vac secondary is super rich that causes miss. Fire gets only slightly better as it warms this is a new carburetor best vacuum is 12 any ideas
Do you have enough advance at idle? At least 10 degrees?
@@NightWrencher have about 14 and total 34 no vacuum advance
Ok, I just gotta ask all the basic questions because some people dont check. Have you tried resetting the idle from scratch? I have a video on it if you havnt seen it
@@NightWrencher going to pull carb and recheck everything mixture screws have little effect cam is 528 intake 536 exhaust, the duration is 221 intake/226 exhaust @.050- 110degrees lobe separation. 10.0:1 compression if this helps
How far open is the primary throttle? I dont think youll need to remove the carb to fix the issue. Is it a 2 corner or 4 corner idle?
Good, something more to check and adjust, maybe))
Actually tons of problems come from misadjusted transfer slot and too small IFRs. Its easy to see on an AFR gauge but hard to pinpoint by ear where the problems are at
Why haven't they made transition reference mark on the external of the carb?
Thats an interesting idea but you can basically eyeball where youre at depending on how many turns you got on the throttle stop. Shouldnt be more than one turm on a stock engine with good timing at idle
My carb won't idle at all. 350 CI SBC with mild performance Lunati cam. Carb is a 650 double pumper with 4 idle circuits. After fixing two leaks, (front Accelerator pump housing and stripped rear bowl screw), it would not idle and just died unless I opened the throttle plates a lot. Also my idle vacuum that was 19 in hg at 750 rpm is now 15 in hg. I had to ask myself what did I change? All new gaskets, new needle cork seals, new needle and seats. But, I later remembered that I had put some silicon grease on the needles and seals to help them go in. That's the only thing different from a normal rebuild, that I did. I now honestly think that the silicon grease and non ethanol gas plus octane booster I run, somehow formed some chunks or goo that clogged the idle restrictors in the metering blocks. So I did a super clean out of all passages but that still didn't fix the problem. I can adjust the screws in to the stops but it still runs, but rough. Probably because it's running on the transfer slots since the idle stop is so far open. I ordered new metering blocks yesterday and will find out if that is the problem. I hope it is because I'm running out of ideas. Great informational video, thank you.
Your engine is supposed to die when you turn in the idle screws all the way in. To me it sounds like an internal leak and its running super rich. I would check 2 things, first, make sure you used the right gasket for the metering block, there are 2 styles, 1 with the hole for the accel pump shot and another with the same hole but its part of the hole for the power valve. Ill upload a picture on my instagram to illustrate what I mean. The second thing I would check is your float height. If its too high or your fuel pressure is a little too high, itll start pouring down the boosters. While its idling carefully look inside the thoats and make sure the boosters arnt leaking. Check those 2 things and lmk. Ill upload a pic on my instagram right now.
@@NightWrencher I closely matched the new blue gaskets to my old black ones. All holes are exactly the same. It's acting like there is zero fuel going to the idle circuits/needles. Starts okay, then idles down and dies. I opened the needles up to 2 full turns out and same thing, until I adjust the throttle stop open and expose the transfer slots. Then it does idle but not like it always used to and the vacuum is 4" lower. There's no fuel dripping from the boosters and it revs great just like before. It never did this before I put that damn silicon grease on the needles and cork seals. I get my new metering blocks in a week and I'll see what they do. Hoping for the best. Thanks for the reply.
Your vacuum doesnt have too much to do with your issue, itll resolve itself when the carb runs correctly. If you pour gas down the throat will it idle for a bit then die or does it make it worse? Also, did you replace the gasket for the baseplate? Some of them are almost exactly the same but the 2 holes on each corner of the main body that feed the transfer slot are offset and will block fuel from being fed into the transfer slot. Also make sure your big vacuum lines for the booster/pcv are plugged while you diagnose your issue. If your passage for the needle and seat are clear, it would be wise to blow out all the passages in the main body just to make sure none of them are plugged. It sounds like the issues are for both front and back so do make sure the baseplate gasket lines up perfectly with all the main body holes
@@NightWrencher By baseplate gasket you are talking about the one between the body and the throttle plate? I did change that and I'll compare it to the old one that was in there. The transfer slots seem to be getting fuel but the idle holes aren't. Sure will be nice to get it running clean and stable like before I rebuilt it. I did blow out the main body holes with 60 psi air. Got some gas in the face and they seem ok. The low vacuum is an indicator that there's not enough fuel at idle. That should come back with the new metering plates and the throttle plate adjusted back to covering almost all of the transitions slots. Thanks for all the replies. I'll let you know what happens.
Yes please, I'd like to know what fixed it.
If I might Add, it is almost as likely that the IFR's are too large, and the flat level steady cruise easy tip-in has a stumble, and the afr gauge shows a 11:1, Then test putting a .01x" diameter piece of wire in both front IFR's and do a test drive. Point is, some stumbles are RICH stumbles from intermittent over fueling. Not all stumbles are lean stumbles, are they? Insult to injury, increasing pump shot in an attempt to remedy an over-rich top-of-transfer-slot, pre-main booster, steady state condition gently transitioning faster, no?
Cool, im glad i found this. Been tuning on my 80 malibu, 383 with a QF670, ive got everything pretty good but at very light throttle, it hesitates and spikes lean to around 16:1. Ive messed with the transfer slot, ive messed with the ifr's. Pretty sure its the transfer slot adj as they are around 60 thousandths. I thought it was due to me dropping to a 30 ifr, but it did it too with a 35 ifr, tells me its the transfer slot.
The transfer slot is non adjustible, only the opening is adjustible which you should have as closed as possible. When it hesitates and spikes, the number you see isnt the exact number since the misfire causes the hesitation which increases the o2 in the exhaust and makes it read leaner than it is. You need to tune based on consistancies so keep the throttle steady in high gear in the transition and read the AFR. If it constantly reads lean, you need bigger IFRs. If your RPMs are too low and the engine is bogging, thatll cause hesistation as well. A lot of things to consider. When I tuned a holley 670 for a 383 last year we ended on a 32 ifr and 70 primary jets. And 50cc accelerator pump with 13 degrees initial timing and 36 total. Good luck
@@NightWrencher It has had this lean spike no matter what adjustment i do, i checked the transfer slot and it was around 60 thousandths. it idles at 13.8, cruise is 13.2-13.5, and power is 12.5. The only time it has the lean spike is very light throttle, like cruising thru a parking lot, when ya let off then ease back into it, it spikes to 16 and hesitates.. its not the acc pump either cause thats on point. anyways thanks for the reply
I have Holley that was rebuilt by the guy that rebuilt my 68 cougar 390 motor, close to stock rebuilt. Engine was dyno on engine stand and broken in. Installed engine, over a year ago, and can not get the car to stop hesitation off the line. Engine guy broke vacuum advance and had a Pertronix 2 ignition system in car. I have tried a lot of things, new distributor Pertronix 3 with vacuum advance, now i have gone back to stock distributor with points and stock coil, I still had the hesitation. We noticed that with a timing light on the coil wire, and vacuum advance hooked up, the light goes out for and instant during acceleration, when vacuum is disconnected, when we give it gas, timing light does not cut out.
I have tried another 600 carb, same results. I have tried set the carb, ideal screws, transfer slot, (not sure if the rear plates are correct), now I can not get the car to go in gear, it idles. Not sure what I did or how to fix this car
I thought I replied to you already, but it looks like it didn't post. give me a sec and I'll go through your post again
Thank you I am going to try agin this weekend to see if I can see anything else wrong on the carb.
Ai also noticed that there is a little gas coming out of i Guess a seal on the side where the throttle arm attaches to the butterfly. Not sure if my kit comes with this seal or if it is possible or mr to replace it
I also have a very small a little bigger than a pin, below my transaction slot, all the outer carbs I have seen have bigger holes, is this where the idle circuit adds fuel to the car. I can send you a picture
@@marionazareth6417 Hi Mario, it sounds like you actually have a reverse idle setup. so that means that your baseplate has that pin hole (same diameter as the slot approx. .030) below the transfer slot- the small hole is the curb idle discharge, and both that AND the slot are served by the same circuit. AND, your mixture screws work in reverse- they actually meter additional air via a 2nd air bleed on the primary bores of the main body underneath the main boosters. so, clockwise adjustment richens, and counterclockwise adjustment leans the curb idle mixture. flip your carb over, open the primary throttle and look to see if you have these extra holes, they are slightly smaller than 1/8 inch diameter. I can explain more off line and I have photos of my carb parts that also are reverse idle
Great info!
Thanks man, that was an old video and I plan to redo all of them with new info eventually
Good explanation, Thanks!!
Youre welcome!
Thanks for the video. Very informative. Should the secondary transfer be set the same way with a little square showing in the transfer slot? Also, could a bad throttle cable setting cause a rich situation? Seems like the idle mixture screws are making no difference and it runs real rich.
Hey, if you have a 4 corner idle carb, you should square up the rear transfer slot and then set the front. If you have a problem with the idle being too rich, run the screws all the way down until they bottom out while the car is running and it should kill the car. If it does not kill it completely you have an internal fuel leak either from the float being too high or having a blown power valve. Check that and get back to me and let me know what you find
One last thing. If you do not have 4 corner idle, the rear blades should be comepletly closed
Sorry bud but I don’t know what a 4 corner idle is? I checked the power valve. It looks fine and it is brand new. I also can bottom out both idle screws and the engine does not cut off.
Well then I think we found your problem. If you only have 2 idle screws in the front, its a 2 corner idle. If it also has 2 in the back, its a 4 corner idle. Did you check your float levels? While running, they should just bearly be dripping out of the sight hole. If you take the sight plug off, only a little bit of fuel should come out. If its pouring out, your floats are too high
It it’s a marine Holley. It doesn’t have site holes or the ability to adjust the float level like that car ones. I checked them when I had them out and they looked level when they were shut.
Thank you for your patience BTW
Sometimes it's the power valve causing an off idle stumble is the power valve is too. If you have a lot of vaccum and a low level power valve you can go up from a 6.5 to a 8.5 and fix the problem.
Actually the PV circuit has nothing to do with an off idle stumble. If you are able to go into the PV circuit off idle then youll be going into it alongside the main jets which also has nothing to do which off idle performance. Fuel from the PV and main jets comes out of the boosters but when you're coming off idle, the throttle plates arnt open far enough to pull vacuum off the boosters and even if it did, fuel would take too long to travel through the entire circuit to make any difference off idle. Off idle performance is dictated by idle screws, transfer slot, IFRs, accel pump cam and accel pump nozzle. Thats it.
@@NightWrencher So you trying to tell me, a ASC Certified Master tech for the last 40 years who has had and raced cars with Holley carbs on all of my street cars and drag cars I don't know what I am talking about?
@@kennywhiddon1497 yeah, basically. Racing a holley and daily driving a holley are 2 different things. You tend to ignore too many things when you can sit on the trans brake at part throttle. If your idle vacuum is at say 18 and you have an 8.5pv installed, you would have to go pretty deep into the pedal or drive a heavy car with tall gears to get your vacuum down far enough for it to open long enough to make any difference. I drive with a vacuum/boost gauge so I see the numbers all day long. My idle vacuum in my LS is 22hg. Driving a stick, with 35 tires on 3.73 gears, the lowest vacuum I see off a stop light is 12hg unloaded and only see 5-0hg when pulling a trailer. The PV circuit just does not respond fast enough to make any difference off idle and I invite you to show me any holley books or articles written by experts to prove me wrong. If I'm wrong, I'm wrong, but there's gotta be evidence.
@@NightWrencher I have fixed more drivability problems with Holley carbs on street cars in the last 40 years than you could ever imagine, not all problems are found in books, people mismatch jets, power valves and improperly set ignition timing and advance curves all the time as well as have the wrong heat range spark plugs. Every thing must work together. By the way, if you are on the trans. brake at part throttle, you must have never heard of a two step. Most off idle stumbles are on cars and trucks with a automatic trans.
Ok but thats not what we are talking about. We are not talking about mismatched parts, incorrectly installed parts or messed up timing. We are talking about the fundamentals of a specific system. We are talking about instantaneous off idle performance. You are stopped, you attempt to go, stumbles, then picks up. A power valve will not cure that. Maybe more timing, maybe wider plug gaps, maybe a bigger pump shot, but thats not what a power valve is for. A power valve adds fuel to the primary circuit. If the boosters arn't flowing fuel, the PV isn't contributing. I can see what you are trying to say, but thats not off idle performance.
Would be nice if they would of had 2 needles, side by side. One for the idle mix (normal), and another on top of it (to set the flow of the transfer slots).
I know that it's more stuff to mess with and get wrong, but oh well
Smart man.
If you drill the idle feed too big, grab a small piece of stranded wire and bend it over in the hole. When you put the gasket on it will hold the wire in place. (An old Holley trick)
Very true. Its much safer to just take it a few steps at a time but you gotta do what you gotta do!
Soy boliviano pido por favor explicación en español tengo el problema del afinado y no puedo haser q funcione en ralenti por fa un número para llamada directa quedaré muy agradecido
Puede comunicarse con migo atravez de instagram @thenightwrencher
Motorcycle carb work slightly different. Lol lots of timers run there car to rich n don't even check there timing. Fyi my Motorcycles don't smelled like gas when i twist the trottle.
very information, that is a huge gasket.
Which gasket are you talking about? 🤔