750 Cross Kart | DUAL CARB Swap + Jetting!
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- Опубликовано: 5 сен 2024
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We're still having terrible problems with our 750cc engine above 7,000 RPM- The lower 2/3rds of the power band feels great, the kart has tons of power, but when you get it under very heavy load high in the RPM range, it continues to break up and lose power. We're still chasing down the issue, so today we're drilling the emulsion tubes on the stock carburetors, and when that doesn't work, we build intake manifolds out of PVC pipe and swap the CB750 engine over to dual 34mm Mikuni carburetors.
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"IGNITION!!!" I really believe you have a spark issue. Breaking up at high rpm its likely the secondary circuit of the ignition coils. I would replace the coils and throw some proper temp and gap spark plugs in. If that doesn't cure or improve even a little then cdi box or stator would be the next step. Make sure the coil ground is good as well as the engine ground. It just really sounds like the spark is falling off under high load causing the break up and limited rpm. Hope you see this and it helps 👍🏼👊
I was gonna say the same thing. Smaller engines have the same problem at high rpm. That's why you can get a plv ignition for predator engines and have less problems getting proper spark at higher loads.
My thoughts went toward the Advancer being the issue. Common issue with these older Honda engines. the springs get weak, so the Advancer isn't pulling in the spark to the optimal 18-22 degrees at WOT. Your thoughts? Zip~
I was going to make the same comment about ignition but it still doesnt explain the wide open throttle issue to me, I do not envy John and Isaac at this point.
Thank you! We figured it out😉 you'll see soon!
@@CarsandCameras Awesome. I cant wait to see that video. You guys have done so much stuff. Its been fun to watch you tinker.
I like it! It's a step closer. Love the PVC piping. Work out the ignition next. Then go back with messing with the fuel. I always hated syncing those carbs.
Had a Cb, ran just like that once the mufflers were removed, I’d strongly recommend an exhaust. Eliminate that first and if it doesn’t work continue with your current method
Big Tony exactly my thought too. I was searching the comments to see if someone else said it b4 me. 2x2-1 would solve a lot of problems.
Agreed
@@keystonerider1308 4 into 1 would also work
When you remove the muffler restriction you'll get more airflow through the engine at top-end which means you need more fuel at top end AKA a bigger main jet
back pressure is your friend
We have a model a 2dr that is in decent shape. Motor and trans was missing when we bought it. We didn't restore it, We rat it out instead. We updated the drivability and stopping. We installed a kz1000 Kawasaki engine in this car. We mated it to a Nissan 5spd out of sentry. It took a lot of bookwork and time to make this happen. Instead of the engine/trans in side ways, we turned it inline. Where the axle shaft went in, we devised a drive shaft to the rear quickchange axle assy. The other a cap and seal. This is a fluid engine. Radiator is needed. Original fuel system was rebuilt and kept stock. Sensors and other portions were replaced before we continued. This sucker is crazy. Motorcycle engines are the way to go in small cars.
Have tried setting spark plug gapping I had similar problem thought it was fuel but it turned out too be spark plug gapping
the little things matter lol
I hope they see this comment
@@killaz123456789100 I do
Tighten the gaps up.
That's true also. If the gap is too big the plug will burn too hot and unless they have a big coil throwing out a major spark having a hot plug gap won't do any good. Also needs mufflers for back pressure
The good fortune of them having John’s father (and mother), such a great father, a) to have the means and b) being nice enough to allow the use of his yard and garage for all of this is simply amazing.
There is another guy on you tube called, Classic octane. He is always working with these old honda engines. I know in alot of his videos he runs the carbs with pod filters with no issues, he also says what jets he is running. May be worth it to check out his stuff for some tips
Steve Godfrey He runs older mechanical slide carbs, not CV carbs. It’s not as difficult to dial them in
he also know what he is doing, and not drilling jets and crap like that.
Also, Put an exhaust system on it, these small engines require a certain amount of back pressure to create vacuum.
Thats a myth. only 2 strokes require back pressure.
4 stroke engines create vacuum on the intake stroke, as the only path for air into the cylinder is through the intake valve and thus through the carburettor. No exhaust pipe needed.
Back pressure is a myth in all engines, exhaust velocity is what you want.
@@rarbaugh07 Two strokes hate you
We all hate 2 strokes so we are even
"It'll be fine" when you add some mufflers...just sayin...
Was thinking about that. For grind hard plumbing co it sorted out their 450. I know its not the same by any means but sometimes the silly things end up being the culprits.
@@safetyboots2642 grind hard had a baffle stuck in their pipe which was stopping air flow.
my thoughts exactly, need back pressure.
i was thinking the same thing
@@jackmehoff2961
No, you don't need back pressure in an exhaust system.
EXHAUST, grind hard plumbing had a very similar issue. they ended up buying a new motor only to find out it needed a factory spec. exhaust system. sometimes uncorking something isnt the best idea. they said it was there most expensive easy fix. lol
Typically exhaust issues are more of a 2 stroke problem... Not always, but most of the time.
What would be right on for a 2 stroke COULD cause an exhaust problem for a 4 stroke though...at certain speeds and tube lengths.
I saw that GH vid and their motor was sounding more like it wss chetting choked where CC's issue sound s more like it scatters when the rpms get up.
use a digital laser thermometer or thermal camers to see which one of the headers are hot and wich not. that way you could see which cylinder is lean and which one rich
Harbor freight has em cheap
A squirt of water on the header tube can tell you alot.
That's how i tuned my old 750 four SOHC , I put a set of smooth bores on it, but it wasn't breaking down ever like that, it would still rev to red line. But it's a great way to set your jetting and not be too lean or rich. I'm afraid these guys are going to cook a valve or piston with all the playing around with the carbs.
I'm thinking it's not a carb problem at all. I think another problem is no exhaust back pressure.
I'd check the ignition coils, plugs and wires, it sounds like one of the coils secondary winding is breaking down.. and the stock carbs are filthy, soak them in some gumout in a ultrasonic cleaner...
@@gooblio yeah
Geez Isaac you look like a mad scientist cutting the pipe.
Dead set on keeping that eye poking phallus, huh?
When John loses an eye over a huge bump, they'll cut that thing down to a reasonable size and put a knob on it. Not before. You can't tell these guys anything at all. How long have we been on them about _trying_ a muffler? Engines are designed to run with specific air box and exhaust restrictions.
He said he couldn't get the butterflies lined up. With a Honda thats everything.
Nothing to see here “it’ll be fine”
@@braapmoto9268 No doubt. That's why we have two eyes. 😜
Nothing to see here one is none, two is one👍🏻
Can't remember if you guys ever did a compression test...? I call this a success at the end of the day fellas! No good idea was ever proved or disproved with out trial and error being involved... I also wanted to take a quick moment to say that everything is really looking and functioning very well! You guys went from chassis build, to trying to get this engine configured into the cart so fast, that i don't feel like you guys were payed homage on how well your guys cart is actually working! Well done!
On the old SOHC 750's, the coils were notorious for going bad.
Guys. Get a infrared temp gun. Test each exhaust tube right off the head and that will let you know which hole is running rich or lean. Synch the air then start checking exhaust temps. High lean low rich.
Or buy a cheap wideband instead of guessing...
We figured it out! It wasn't the coils!
@@CarsandCameras what was the issue?
That's not a SOHC that's a DOHC sohc didn't have diaphragms on the carbs
Run your engine with a new spark plug for long enough to warm up, and run it at the rpm range your testing for, shut it off and remove the spark plug. the color of the residue will tell you for sure, if it needs a larger or smaller jet. This method of tuning is old-school, but it works. One more thing I wanted to say about tuning is that unless you have increased the cubic inches by boring out the cylinder, or a longer stroke crank, changing to a larger carb to increase power usually has the opposite effect because the larger carb will have a lower velocity air flow, which screws up all your jet settings, and causes dead spots between circuits. Hope this helps, love that 750, don't over-carb it, your best build ever. PS like to see you put a predator212 on a mountain bike, and see how close you can get to motorcycle performance.
Whats up with the right front wheel trying to live stance life??? Ya'all tree it already??? lol
Guys, the "horror music mad science" sequence is the best thing you've ever done from a production/art standpoing. Fantastic! :D
i have a feeling its a valve clearance issue, also i'd check the compression, check the timing with a light, i think it should scream with the dual carb setup.
i agree, many years ago i saw the dual cam 750/900 engines with valve clearance issues, to the point of burned valves...
I said the same thing 3 days ago the valves tighten up over time holding the intake open, causing back pressure in the carbs
rory fontana .
Fell. Asleep with my hand on the keyboard, sorry!
I agree 100% I have an 83 gs850 that ran that way too long and burnt the valves. I checked clearance and it was less than none. Made it 45,000 miles tho.
Time to invest in a wide band O2 sensor. Specifically to debug situations like this.
Good idea, we just got one the other day!
Looks like he damaged the right front wheel... Looks like it has way too much camber now
ChrisEsposito I was gonna say something about it I noticed it and was about to comment before I saw this
Coils and leads guys. Check cam timing aswell this can also put timing out and restrict air flow. This old 750 were known to skip timing on cams especially with some miles on them at high rpm. Put the old carbies back on with standard jets. Check the idle ports in old carbies and float levels. Some back pressure would help too.
Time to start checking timing and spark quality. One of your setups should have been close enough to run it into high rpms. I had a 850 Suzuki that had a junk stater was just putting out weak spark spent all winter fooling with carbs.
To me, it sounds like the ignition timing is out when it gets to the higher rpms. Do these engines have anything that automatically advances/retards the timing in relation to load/rpm?
Oops, that post was supposed to go in the main comment thread. 🤦🏼♂️
Been watching for at least 6 months now and finally got to where i see y'all stuff when it comes out. I looked so forward to today's video for example! Love ya both, keep it up. This is new school entertainment...at least thats how i put it!
Boys, 1 and 4 are most likely lean. "Y" the intake manifolds for even delivery. And yes, get some mufflers on it.
Add some exhaust, check the spark plugs, the gap and the overall condition of them. Coils could very possibly be the issue, but it's not really likely given the symptoms. If the coils were going bad, it would usually start breaking up almost immediately upon acceleration... especially once the the engine gas gotten hot. The same can be said for the ignition modules. Keep in mind, I'm no expert, but in my experience that has been the case. And usually it's the simplest things like not having that exhaust, or having fouled or dirty plugs that can give you the most fits. Good luck. I love the build so far.
Sounds like you should put some kind of exhaust probably doesn't have enough back pressure
The guys from grindhardplumbing had the same issue with a 450 kart. As soon as the exhaust went on it ran like a champ.
@@brettcanosa3601 That was taking the exhaust off... they took the baffles out of the exhaust and REDUCED the back pressure not increased it.
great project love it just thinking you might want to look into a Y pipe to split both carbs. As the T fitting helps the middle 2 flow as the outer carbs get less air. This becomes more pronounced in the high revs
Too smooth intake runners or ports wont make an engine run that bad. Too short exhaust or air filters wont either. Maybe the problem is in the engine itself. Maybe test compression and valve clearance first. Carb should be fine with stock jets if everything is proper. Good luck
I have a 71 cb that I'm looking to get running again so all of these videos are not only entertaining (because cross-kart) but informative as I still have some tests I need to run on that motor. Keep it up guys!!
Look into a full size fuel filter for a car that will last longer than a little Briggs filter.
Personally with gravity feed I'd prefer a strainer/screen or sedimenter setup over a "proper" filter since they can be so restrictive to flow. At the end of the day, you're in control of what you put in your tank & clean fuel in = clean fuel out.
Gotta put the mufflers back on it. They're tuned with the airbox and mufflers installed. Open pipes tend to lean em out.
Get pods for each carb and tape them 3/4 the way up and it needs the muffler for the back pressure
Back pressure hurts performance. They need headers for the exaust from one cilinder creating a vaccum and pulling the exhaust gasses faster from the other cylinders.
But with the muffler off it should still go to full 9500rpm the pods might be on to somthing there
@@duckytheduck3127 Wont make the engine run that bad.
@@duckytheduck3127 cutting out at 3/4 throttle hurts performance
@@duckytheduck3127 u sir have no idea about anything
It's the Venturi effect.
If you made a plenum (chamber) for the carbs to filled and plumed from the chamber to the intake ports. you won't be robbing the two cylinders of air & fuel on high revs.
is that a round about way of saying it needs a common rail.
Good point, I'm making steel manifolds for it
@@hunter100t It has Carburetors not a fuel injection system,
The two cylinders inline with the Carbs on high revs will suck the air flow backwards from the two outside cylinders because rapid air & fuel passing through the T fitting causes a vacuum. It's a Venturi valve.
So to be able to stop the carbs playing favorites with the cylinders, a space between them needs to be made. That Fuel & air can mix around and fill. The cylinders can pull from the space when they need too
@@CarsandCameras Are you still thinking of what you can build with Yamada 18hp diesel engine?
It should have tracks.
I'm with you. I think you are not getting a proper spark at high RPMs. I do think you need to redo the compression check and have a look at your plugs. If it's running lean at high RPMs the plugs will tell you.
I love the dual carb setup. Getting rid of those CVs has to help. Just fab up a proper Y shaped intake.
Coil gap
Isaac will figure it out he always does, he is a complicated guy lol. I know you guys will come up with the right answer it just takes a little time to figure out the air to fuel ratios and if the ignition coils are bad and the sparkulator is sparkulating. LOL Shade tree Humor. but It'll be Fine guys. You are teaching a whole new generation of guys and gals how to do things with their minds and hands. That's why I enjoy watching you videos. Faithful Subscriber from Southeast Missouri.
I don’t see a issue with the dual carb pvc intake ( hit the inside of the runners with some 36 grit) I feel it’s a ignition issue for sure
Depends on whether or not the fuel is melting the PVC. If not I'd prefer a setup where the intake runner length is mostly the same, with the current version the inner two cylinders have a straight shot from the carbs while the outer two have two 90 degree bends between the intake ports and the carbs. There's no way the flow between all the cylinders is balanced.
@@butchs.4239 if they put the carb between the two then put 45 bands it would probably be better
@@phoenixeragon6404 Exactly. Issac made the comment about having to support the carbs if using a long runner y-pipe intake. I'd agree with that, but if they're trying to keep the runners short and the carbs close to the motor they need a T fitting and two 90 degree elbows similar to how they did the single Mikuni intake. That way the runners are close to the same length, and each has a bend in the airflow so the cylinders should be well balanced.
Maybe some turbos will help?!?!?🤔
Maggie The Farm Truck I was thinking 4 😂
Aiden Hopkins would be awesome, but what if they do dual carb/dual turbo set up🤔 that would be sick.
Yup bit a nitros to 😂
DEFINITELY
they should try to find gpz 750 turbo it would rip
I must say, one of your videos is a very nice birthday present for me ! Turning 16 today !
Enjoy the next two years
Happy birthday
@@propaneandpropaneaccessori3446 ty man XD
@@isaacitllbefine7231 the man himself responded to my comment, well fuck now it's an even better gift !
I vote it’s time for the 4 into 1 exhaust! Or at least 2 into 1 each side for duals. It will be much easier to tune I bet.
Also, get some copper, galvanized, or light wall stainless steel tube of some kind to replace the pvc.
I have melted pvc intake tubes before just like this haha! They do work for testing though!
I’m loving the progress guys!
The throttle response was pretty nice with the dual carb setup!
I’m wondering if the duals will flow enough air for all 4 cylinders, but it did sound much better than before!
I had a similar problem with a 86 Honda shadow I had a few years ago and it was the coils just not firing hot enough
Ours are still original, but it turned out to not be coils!
400 Carter AFB (Aluminum Four Barrel) mounted to a CUSTOM Intake Manifold?
With the Carburetor above the engine...
Still SO JEALOUS of this build! 🙀
Take care,
🤓 -Thomas
Western Washington State
Issac: We need to get a heat shield going on this thing
*3 episodes later*
Issac: I think we should put a heat shield on the kart
I had a 1983 cb1000 with 4 k&n pods and a 4 into 1 header. It ran awesome with that setup but every now and then it would foul a plug and only run on 3 cylinders. The way your car is sounding in this video is exactly how my bike sounded when it was running on 3 cylinders
Mario kart is looking great
I agree with everyone about the ignition coils, might also want to check the points. The dual carb setup seems like the way to go but, when you're done testing it you guys might want to make a Y shaped intake runner for each carb. The way it is now you will starve 1 and 4 while 2 and 3 are running rich. Just my 2 cents. Great vids guys, love watching your stuff.
I was almost yelling at the screen, from the first time I heard it run. "Weak spark". Other than that, I liked it. Thank you for the entertainment.
I totally agreee
the poor spark plugs are prolly killed with fuel
I can’t wait until you get the engine to run on full throttle so you can get onto adding paddle shifters. Lol. My lord that shifter looks bothersome. Keep up the good work guys. This stuff is gold!
@15:54 I swear it sounds like one cylinder has no compression while you are turning it over. Have you done a compression test?
Mitch Thompson or spark ⚡️
You guys are awesome. It's so fun watching your RUclips channel channel.
Also good job guys, oh it might be timed wrong on the higher end of the rpms
Also a thought of mine.. could be slightly pre det at top end
FunkyQuetzalCoat126 yeah, but pinging sounds different and if it is using an older coil then it could missing at a higher rpm, I’m pretty sure my moms rm 85 does the same thing in mid range
@@justinchain1668 so throw a new coil on it and some fresh wires ect?
FunkyQuetzalCoat126 not yet
@@justinchain1668 yea dude just put a new coil new wires ecu on and on they will get it eventually
Man I loved that mad scientist montage!
Front right wheel has a lot more camber then the left
I know right 😂???
All the vintage Japanese bikes I’ve owned had carb issues and if I was smart would have bought new ones for all the hassle they were. Your mods make it look scary fast
It sooooo sounds like coils/cdi :) awesome though!! Love your stuff!!
Y'all need to use a synchronmeter for motorcycles. They are typically '4 channel'. The single cylinder synchronmeter you have works just fine for cars with higher displacement but not sensitive enough for your small displacement 750cc. Your local motorcycle shop will hook you up and show you the light...its so simple...less carbs is not the answer... just get the right tool. Keep up the good work.
Can the guy in the hat please say “damn it Bobby” in the next vid. Thanks.
That's ike
Very cool diy intake. A longer intake runner made of steel tubing shouldn’t stress those bolts out too much, I reckon. The only thing holding y’all back is the ignition system. If that don’t wake it up any then maybe y’all have a compression issue. Keep up the good work!
hey Isaac. 3:40. you missed a hair while shaving :-D
Been there, done that...
lol saw it too
I like it,,,,,,,,, looks fashionable.
Saw that too. Lol
Hear me Out! I’m pretty sure this is a 1981 750CB K. They have a gasket operated squirter pump that injects more fuel to the front of the throttle plates. There is an additional cable attached to the throttle that connects to the fuel squirter just like a car carb has. There is a black adjustment knob on the bottom to adjust the squirtiness. If the diaphragm is not good it will let extra air into the squirter rail that is before the choke plate on the intake. The vacuum leak idea and lean is right the squirter is adding the extra fuel it needs past 1/2 throttle
You must have the most understanding neighbours on the planet......I need to get me one of those, do you make them to order? Ship to the UK maybe?
Word
True. My neighbor is yelling at me because Im watching cars and cameras videos too loud in his opionion. lol
I got to fight my neighbor over a rc truck lol
I got told my yard not a stadium its a residential neighborhood tired seeing flying rcs out his Windows
Hahaha we do have AWESOME neighbors
Just a note drilling out the emulsion tubes only affects the fuel in your 1/4 to about 3/4 throttle range because that is where the needle is in charge of the fuel and then from about 3/4 to full throttle is the main jet so if you are having a problem with fuel from around half to full throttle then look at needle position and bigger main jets. The main jet will have a smaller hole than the emulsion tube so if fuel at full throttle is a problem then just slowly keep drilling out the main jets till you get where you want to be and it is possible to tune it for the open headers and pod filters and make it run right as this is how a lot of drag bikes are run. With the wide open exhaust it allows the exhaust to escape very fast and can cause it to run lean as well thus go bigger main jets or put some sort of restriction on the pipes. It also wouldn’t hurt to make sure that your coils are on good shape start by doing a resistance test on them for the primary circuits and then the secondary circuits and then make sure they are not shorted to ground also make sure the body of each one is not cracked in any way then finally check the plug leads for spark leaks as well. Ps the plug leads can also be checked with a multi meter for proper resistance. Good luck and just keep doing you it is what makes the channel what it is.
When you were synchronizing the carbs on the last video one had a fluctuation. valve, tappet, flat cam lobe?
I also noticed that..
I remember watching an episode rather B welding, he was having troubles with his engine with the new build as soon as he added dual exhaust the motor was happy as hell
I think you may need more back pressure, try exhaust system. Good Luck!!
Oh man - how happy you guys were to fab intakes out of PVC...that’s the stuff that makes this a favorite channel 👍🏼
Sometimes an engine needs a little back pressure with the exhaust. Just saying
Ken Mullins back pressure is a myth, just needs headers that are a good diameter for that motor, it’s not much displacement so a small diameter pipe would allow the exhaust to scatter better
I would try dual 38mm carbs and get some UNI air filters. They are just like the K&N filters, but they are foam. The K&N filters are known to restrict the air flow a lot.
For the forth time.... IT NEEDS A GOD DAMN FUEL PUMP!
maybe maybe not, are you sure, you don't sound convinced lol
@Skott at high RPM gravity isn't enough to fill up the carbs. The bike this engine came from has a fuel pump originally.
Yall inspired me to make my channel where I make videos on all kinds of small engine vehicles. Keep up the good work guys. Great videos.
You are running straight pipes. Zero engine back pressure. Could be several small problems together
back pressure is a myth ...just ask uncle tony
Al T back pressure on cb750 is not a myth. Try doing homework buddy
@@zethloveless7238 lol...well it seems to work on top fuel dragsters ...among other things
Al T taking off stock mufflers on a cb750 can cause it to run lean. Would need to add more fuel. Not saying you can’t run straight pipe you just need to address the problems it causes
@@zethloveless7238 wow...so upping the jet sizes will fix that ...and it seems to have solved the problem didn't it ...get a fucking grip adding a full exhaust won't solve the issue ..the issue is more likely ignition let the boys fix that before filling thier heads with stupid redundant ideas
Guys, yeah, ignition. I had exactly the same problems with a Yamaha xs850 - breakup over 4000rpm - and it turned out to be the old original ignition coils failing. I swapped in 3 Suzuki samurai coils, that was in 2010, and its run great ever since. Try it, trust me.
I'm no expert butt.... the free flowing exhaust (no mufflers) the high flowing air filter pods or your air box, youll need aftermarket jets. bigger mains and pilots. I'm sure dyno jet still makes a jet kit for it. I had a 95 fzr1000 with the same problem, breaking up in high RPM
I am an expert butt...
I know you're reading the comments, so here's my idea: With so many carburated engines you have around, get a wideband o2 sensor. You can weld a nut in any exhaust header and put the sensor in whenever you need to do tuning. You'll find them for around 200$, which is a lot, but could save you a lot of time and frustration.
Pull the plugs out you’ll see if your to lean or to rich
Justin Hunt it’s like people don’t understand how to read a plug. Put some fresh ones in, run it at full throttle and pull the plugs to see if you’re lean or rich 😂
Hey guys just wanted to say congrats on hitting 700k you guys deserve it 👍 please make a mean sized crawler!
Remember, I work at eBay's largest used motorcycle parts dealer, MRC cycle, and offered to sponsor you. We've got TONS of engines
Are they AFFORDABLE...? ~( ,m,)~
You guys buy enginges i have a trx 450
Have any 50cc 2 strokes of parts? I'm cooking up something crazy.
@@rcplayer7581 not really
@@mathdebates7936 moped or shifting?
Amazing build and congrats on 700K. 1M right around the corner.
Thanks!!
The old carbs are most likely fine they just need bigger main jets there’s to much air not enough fuel
Its 2 rich
Have a read up about air boxes. Has to be set up in a way that all carbs get equal air. And if there is a intake only on one end, that carb closest will draw the most air. You need a tapered air box that is big enough. Or single filters on each carb. Hope you can read this.
It sounds like it's on 2 or 3 cylinders
Ya it does. Thats one odd sounding 4 cylinder. Unequal length headers (subaru sound) maybe?
My manlift/cherry picker has a Ford pinto 4 cylinder that when it's cold it is the same way but I can unplug the middle 2 sparkplugs and 8t doesn't change I think cracked distributior cap
@@screamin4402 check valves.
It just doesn't run correctly but it changed a lot for the better with 2 carbs.
I'll agree with the others saying you need some back pressure in the exhaust. If you want to keep it open pipe loud just find some thick washers with the same OD as the pipes and weld them to the open end of the pipes. Drill them out as needed to adjust the amount of back pressure created.
Hey guys Isaac and whatever try changing the spark plugs NGK racing plugs
Yeah, my cb750 nighthawk is super picky about plugs. the standard NGK copper plugs work best. Iridiums don't throw a hot enough spark, copper cores are best.
Check the timing and the clearance on the points. they might need some fine tuning or they could be getting weak and need replacement. My 1979 gs850g had this problem and it fixed my issue.
two aspects:
let a dude print the intake of a 3d-Printer... it works great!
the right front wheel has a lot of camber!
You need someone who can print in a material that will cope with heat and fuel exposure. Nylon 6-6 works.
@@Turbochargedtwelve we used PLA and it worked great. I would try to support the structure with some feet caused of the mass of the carbureto. We have a 19mm carburetor mounted with pla with a lever of 100mm without support and without problems moving the bike off road
22Steez PLA will melt in the sun on a hot summer day.... it’s good “for testing purposes” bu I wouldn’t expect it to last long.
@@Turbochargedtwelve Exactly, PETG is better suited for chemicals and heat not to mention its stronger
Lol i am not the only one who noticed✋
Dude John I love how creative you've gotten with the music for the show it's awesome and funny and as for the cross kart just try to replace the ignition system and plugs even though I think you guys changed the plugs already wouldn't hurt to do it again and check the old ones cause I don't think it's the carbs anymore it's got to be spark it's almost the the spark plugs are getting blown out at high rpms like they would on a turbo car with to much gap
Please try adding mufflers! It probably needs back pressure
Try moving the coils to a location on the frame. If that doesn’t work, grab a pair of late model Harley coils. My 80 CB650 (which also had a very minimalist exhaust, sidenote) had similar issue due to poor spark, got a wild idea to throw HD coils on it, had to do some custom fabrication to mount them, but afterward checking the spark it was super bright and huge spark. Tested with stretching the gap out, took a regular plug and broke the tang clear off and it had enough power to jump all the way across the plug, from center to edge, still bright and powerful. My CB650 ran awesome after that.
Ok guys great vids. You need to chuck some mufflers on it, or go way over on the jetting- though you will push the flat spot to mid range wth the bigger jets. Keep up the good work.
Definitely sounds like there is a timing/valve issue
I think the valves are floating, weak springs.
We already checked the timing, it was fine🤷♂️
Did you test the valve springs though? I have a suspicion they are weak.
Great build guys! But don't give up on the 750! Really check the ignition out! The 4s can be finicky about timing! You gotta to see it through! imagine how that 9200 rpm is gonna feel!!!
C&C: (goes offroad) (doesn’t get stuck)
Me: how?
As Jeremy Clarkson would say... MORE POWERRR!!!
I don’t know if it’s been mentioned yet, but for you gas tank straps you could use ones from an LP powered forklift. Quick and secure.
I think y’all are on to something with ignition problems.
At this point it has to be!
CarsandCameras Whenever it starts braking up it always sounds the same no matter the carb set up, maybe weak coil or a braking down plug wire 🤔 wires would be a cheep and easy thing to try. I Look forward to your videos every week!
MAD ISAAC the mad scientist. I love you two
It's running on three cylinders you've got a bad coil.
You could really tell 1 cylinder is not running right when it first ran with the 2 carb setup, sounding like a harley.
Bad secondary circuit (for high rpms) on at least 1 coil...
Turns out it was actually running on TWO cylinders at times
@@CarsandCameras ignition module or pulse generator?
Set valve lash. Dynojet kit in the original carbs after they have been sonic cleaned or dipped for 24 hours. Do the coil relay mod so the coils are getting a full 12v. If you cleaned the carbs with carb clean and compressed air they are not clean enough. I have rebuilt several 80's inline 4 bikes. Your entire issues will go away after doing the carbs right and getting the exhaust sorted.
Seems like you've been missing back pressure since the exhaust was removed you may want to see if that fixes some of your other problems
It'll be fine. We figured it out
I love the music playing while Isaac is making the intake! Lol
Is it me or is the right side front wheel Cambered (bent) out more than the left?