How And When To Change The Jets On A Holley Carb
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- Опубликовано: 10 сен 2024
- Holley explains how the main jets on a four-barrel carburetor operate. They also give instructions on changing the jets for increased performance. The video explains the various jet sizes, and how they affect engine performance.
Why are all these Holley tuning videos cut short? And is there a place to find them in their entirety?
Are both jets supposed to work at the same time? For a 2 bbl? Or is one a idle jet and the other a main jet.
Is there a second part to this, or...?
What about squirter size? Pump cam size/adjustment when tuning a carb? Also what about those things with temp/altitude changes?
Also for jet size you say what to change for temperature decrease, but what about temp increase? You say to change jet size one number higher for every 35 degree drop in temperature from 70 degrees.. but what about increase in temp? Like where I live down here in the gulf south, the temp can range from 70-100+ degrees from mid day to night time and from spring to summer..
So say you’re at the race track on a weekend in June, say that during the day it was 90-95* outside mid day during test/tune &/or time trials, say that on your 750 double pumper w/o a power valve you was running 72/78 jets, 32 squirters, pink pump cams set on the “second hole”... later that night during eliminations the temp has dropped from 90-95 at noon that day to 70* at 9pm when elimations start.. do I go down a jet size? To maintain e/t consistency... Also how do you determine jet size changes by temperature when not running a power valve? Or does that matter? Also what about squirters, pump cams, and other adjustments/changes for weather etc?
I'm here in Mississippi..gulf coast..100 degrees in summer...high humidity....less air = less fuel ...the better the air less humity the larger the jets size...
Or just hit the kits of N20...a little more..lol....
I'm having a rich run at idek problem..air bleeds...has 70 s in idel now..looking to change to 73-75..
33 in main bleeds maybe jump up a few there to... installed a bigger solid cam last year ..now I can only run the idle screws out about 1/2 a turn..before it's runs to rich and stalls the motor...floods out..plugs are black.....so she needs more air for sure....we run at gulfport Dragway...wendsday night's.....
Black sheep is my car..78 GrandLeMans big tier half back car..
360 chevy...I might main jet it down to see if it picks up.... haven't been running alot due to an old neck Injury that's acting up...plat with four screws in my neck....
Keep us posted of any improvement and charges made
Thanks Don.....
Holly 4150 tuning secrets is the vid..good info...
You can change valve lash...as well iv heard of guys doing that to.. another thing to check out...for consistency...at the track......
I dont play around with my car at the track easyer to adjust dial in..lol..if the car is picking up..change dial in number..a few 10 ths ...why work on the car to account for weather..???...it's never gunna be perfect...just follow the car not chase the tune.....it's all a guessing game....when ya change stuff just another equation to guess at...my theory ,,,,kiss ,,,,keep it simple stupid....and have fun..win or lose...luck plays a big part as well...it's not all skill and tuning...in my opinion anyhow...but hay what do I know right...I'm no expert....good luck with it all..see ya at the races man......
So I have a 390 fe pretty stock motor has a 4160 street warrior on it and the mixture screws are almost all the way out and it runs super lean my plugs look white I’m pretty sure there’s no vacuum leaks the manifold was recently installed and I had this issue before,it doesn’t act like a motor with a vacuum leak and it seems to be a healthy motor other than the fuel issue so I guess I’m just wondering why it might seem that I need more fuel?
Also should note when it’s cold once the choke opens fully I have to pump the pedal to keep it running till it’s warmer or it will die
Better late than ever... your 600cfm carburetor seems to be on the small side for that 390 engine, look into the fuel circuit called "Idle Feed Restriction(IFR)". Its located in the primary metering block and it controls the amount of fuel in conjunction with the Idle Air Bleed(I-AB) located in the main body at idle. The IFR is apparently to small, if it was the correct size for your engine, the most you would have to turn the idle mixture screws is about one full turn out from seated. Of course other factors you have to bear in mind is correctly setting the initial timing and idle rpm, you should have gone with at least a 650cfm to 750cfm(prefered) for that engine. You would have had a better chance of it running much better out of the box, but not perfect, because you would still have to tune it to your particular engine. If you choose to stick with the 600cfm carb, you will have to enlarge the IFR restrictor(2) thats pressed in from holley, you can do it yourself but you might go too far, then you will have to drill the entire restrictor out, then tap it to be able to screw in adjustable restrictors , or you could just buy a billet metering block(prefered) for the 600cfm/4160 carb thats has all the adjustability built into it and just buy different sized restrictors for it. Then use an AFR/WIDEBAND 02 gauge to help you dial everything in, its definately a process, but in the end, it'll payoff if your are patient enough to make that engine run as it should or at least how you'd expect.
well, i've got a problem , when i pull the gas pedal more than half ( just when all 4 bbls go open) the engine coughs , what can cause this?
@Real Talk with Aaron thanks for the answer
Too light of vac secondary spring
I'm guessing the video is taken from a longer video about carb tuning and they just cut and chop out sections for each individual topic, you're welcome.
If you have to change by 8 or 10 jet sizes well as Doug Richmond would say "someone's lost the rabbit in their tuning efforts"
nice goat - Bandimere 71 / Topeka 75 - does that make sense ?
Moah 4 Powah
All your videos cut off early
Some look lean and some look rich, then what?
It most likely means your fuel isnt moving theough your intake evenly. Get a 1" carb spacer and try again. I suggest a hvh super sucker. They atomize the mixture really well. A little pricey but worth the money cause you get an even amount of fuel in every cylinder. Try that and then check your plugs again.