750 Cross Kart | DUAL CARB Swap + Jetting!

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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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[@jasonolson3322]

"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 👍🏼👊

[@blackice8705]

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.

[@ZippoVarga]

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~

[@ThatEngineerDad]

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.

[@CarsandCameras]

Thank you! We figured it out😉 you'll see soon!

[@MikeZ32TT]

@@CarsandCameras Awesome. I cant wait to see that video. You guys have done so much stuff. Its been fun to watch you tinker.

[@billcohnen6326]

Also, Put an exhaust system on it, these small engines require a certain amount of back pressure to create vacuum.

[@TangoOne]

Thats a myth. only 2 strokes require back pressure.

[@LemmingGoBoom]

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.

[@rarbaugh07]

Back pressure is a myth in all engines, exhaust velocity is what you want.

[@tebibyte2357]

@@rarbaugh07 Two strokes hate you

[@MrCrazyking81]

We all hate 2 strokes so we are even

[@bigtony8978]

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

[@keystonerider1308]

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.

[@joshmoles3833]

Agreed

[@thatbuelldude189]

@@keystonerider1308 4 into 1 would also work

[@dallasfingrocks]

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

[@jjecarte]

back pressure is your friend

[@pathbelow6652]

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.

[@levelupbytyson5451]

Have tried setting spark plug gapping I had similar problem thought it was fuel but it turned out too be spark plug gapping

[@mehgusta]

the little things matter lol

[@killaz123456789100]

I hope they see this comment

[@greenmountainsuriving]

@@killaz123456789100 I do

[@crazyasspotter]

Tighten the gaps up.

[@Rocketman442-RC]

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

[@geecee4]

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.

[@steve310t]

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

[@preez77]

Steve Godfrey He runs older mechanical slide carbs, not CV carbs. It’s not as difficult to dial them in

[@MrGixxer1300r]

he also know what he is doing, and not drilling jets and crap like that.

[@Buck1954]

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.

[@batsoupbukake7057]

"It'll be fine" when you add some mufflers...just sayin...

[@safetyboots2642]

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.

[@luccaspenceley2366]

@@safetyboots2642 grind hard had a baffle stuck in their pipe which was stopping air flow.

[@jackmehoff2961]

my thoughts exactly, need back pressure.

[@Xer0Hypnotic]

i was thinking the same thing

[@derschwarzgeist]

@@jackmehoff2961 No, you don't need back pressure in an exhaust system.

[@williamstamper442]

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!

[@khrprod]

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

[@leskobrandon538]

Harbor freight has em cheap

[@liljohnp132]

A squirt of water on the header tube can tell you alot.

[@gooblio]

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.

[@leskobrandon538]

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...

[@khrprod]

@@gooblio yeah

[@michaelwoodsdale460]

Oh man - how happy you guys were to fab intakes out of PVC...that’s the stuff that makes this a favorite channel 👍🏼

[@ChrisEsposito]

Looks like he damaged the right front wheel... Looks like it has way too much camber now

[@Lance_59]

ChrisEsposito I was gonna say something about it I noticed it and was about to comment before I saw this

[@ErvahNoir]

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!!

[@lawrenceveinotte]

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.

[@Fontanamotorsport]

i agree, many years ago i saw the dual cam 750/900 engines with valve clearance issues, to the point of burned valves...

[@pkuudsk9927]

I said the same thing 3 days ago the valves tighten up over time holding the intake open, causing back pressure in the carbs

[@fofosu]

rory fontana .

[@fofosu]

Fell. Asleep with my hand on the keyboard, sorry!

[@andrewfortier88]

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.

[@jeffyates4813]

Geez Isaac you look like a mad scientist cutting the pipe.

[@hicksvilleshick]

Whats up with the right front wheel trying to live stance life??? Ya'all tree it already??? lol

[@Grungydan]

Guys, the "horror music mad science" sequence is the best thing you've ever done from a production/art standpoing. Fantastic! :D

[@nothingtoseehere4026]

Dead set on keeping that eye poking phallus, huh?

[@byron7165]

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.

[@motomatt6099]

He said he couldn't get the butterflies lined up. With a Honda thats everything.

[@braapmoto9268]

Nothing to see here “it’ll be fine”

[@nothingtoseehere4026]

@@braapmoto9268 No doubt. That's why we have two eyes. 😜

[@braapmoto9268]

Nothing to see here one is none, two is one👍🏻

[@mowler8042]

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

[@Vintageguy73]

On the old SOHC 750's, the coils were notorious for going bad.

[@tommarkovich6720]

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.

[@Chris-yy7qc]

Or buy a cheap wideband instead of guessing...

[@CarsandCameras]

We figured it out! It wasn't the coils!

[@fidenziogarza1388]

@@CarsandCameras what was the issue?

[@nielsenl4171]

That's not a SOHC that's a DOHC sohc didn't have diaphragms on the carbs

[@todorow22]

Time to invest in a wide band O2 sensor. Specifically to debug situations like this.

[@CarsandCameras]

Good idea, we just got one the other day!

[@ruubjumper126]

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

[@1775bobcat]

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

[@jeffrey717]

Boys, 1 and 4 are most likely lean. "Y" the intake manifolds for even delivery. And yes, get some mufflers on it.

[@Jacksonkellyfreak]

Gotta put the mufflers back on it. They're tuned with the airbox and mufflers installed. Open pipes tend to lean em out.

[@EdWolfram]

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.

[@TheGreyTest]

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?

[@TheGreyTest]

Oops, that post was supposed to go in the main comment thread. 🤦🏼‍♂️

[@ejs6097]

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!

[@jacobford5529]

Sounds like you should put some kind of exhaust probably doesn't have enough back pressure

[@brettcanosa3601]

The guys from grindhardplumbing had the same issue with a 450 kart. As soon as the exhaust went on it ran like a champ.

[@LemmingGoBoom]

@@brettcanosa3601 That was taking the exhaust off... they took the baffles out of the exhaust and REDUCED the back pressure not increased it.

[@theirishaxe9405]

Hey guys just wanted to say congrats on hitting 700k you guys deserve it 👍 please make a mean sized crawler!

[@cole33333333]

When you were synchronizing the carbs on the last video one had a fluctuation. valve, tappet, flat cam lobe?

[@ratman5727]

I also noticed that..

[@TylerDWard]

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

[@Archermboi]

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

[@butchs.4239]

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.

[@phoenixeragon6404]

@@butchs.4239 if they put the carb between the two then put 45 bands it would probably be better

[@butchs.4239]

@@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.

[@lordliam8816]

Ike, the mad scientist!!!!

[@allenmckinney9533]

Look into a full size fuel filter for a car that will last longer than a little Briggs filter.

[@danmackintosh6325]

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.

[@robbovius]

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.

[@disabledede1818]

Get pods for each carb and tape them 3/4 the way up and it needs the muffler for the back pressure

[@duckytheduck3127]

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.

[@killaz123456789100]

But with the muffler off it should still go to full 9500rpm the pods might be on to somthing there

[@ruubjumper126]

@@duckytheduck3127 Wont make the engine run that bad.

[@flhusa1]

@@duckytheduck3127 cutting out at 3/4 throttle hurts performance

[@redneckswitwheels]

@@duckytheduck3127 u sir have no idea about anything

[@cesarpena1392]

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.

[@MegaKencam]

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.

[@williamstamper442]

Coil gap

[@MTFT_atomicgarage]

Maybe some turbos will help?!?!?🤔

[@aidenhopkins4421]

Maggie The Farm Truck I was thinking 4 😂

[@MTFT_atomicgarage]

Aiden Hopkins would be awesome, but what if they do dual carb/dual turbo set up🤔 that would be sick.

[@aidenhopkins4421]

Yup bit a nitros to 😂

[@CarsandCameras]

DEFINITELY

[@hommyy-c5494]

they should try to find gpz 750 turbo it would rip

[@mitchthompson3246]

@15:54 I swear it sounds like one cylinder has no compression while you are turning it over. Have you done a compression test?

[@josteincarlsen2905]

Mitch Thompson or spark ⚡️

[@DerKrawallkeks]

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.

[@brandons.9731]

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

[@CarsandCameras]

Ours are still original, but it turned out to not be coils!

[@kennethdispain1807]

can't wait to see that bad boy full throttle love watching you guys

[@matthews852]

Can the guy in the hat please say “damn it Bobby” in the next vid. Thanks.

[@TheBunnyDeveloper]

That's ike

[@wwilkins62]

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.

[@eriknulty6392]

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

[@DeliciousDeBlair]

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.

[@Steelythestacker]

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.

[@CrazyWillification]

Amazing build and congrats on 700K. 1M right around the corner.

[@CarsandCameras]

Thanks!!

[@justinchain1668]

Also good job guys, oh it might be timed wrong on the higher end of the rpms

[@killaz123456789100]

Also a thought of mine.. could be slightly pre det at top end

[@justinchain1668]

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

[@killaz123456789100]

@@justinchain1668 so throw a new coil on it and some fresh wires ect?

[@justinchain1668]

FunkyQuetzalCoat126 not yet

[@killaz123456789100]

@@justinchain1668 yea dude just put a new coil new wires ecu on and on they will get it eventually

[@thomasbarnardjr9657]

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.

[@Extrmmitch]

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.

[@hunter100t]

is that a round about way of saying it needs a common rail.

[@CarsandCameras]

Good point, I'm making steel manifolds for it

[@Extrmmitch]

@@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

[@Extrmmitch]

@@CarsandCameras Are you still thinking of what you can build with Yamada 18hp diesel engine? It should have tracks.

[@maxbelikov3571]

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

[@22Steez]

two aspects: let a dude print the intake of a 3d-Printer... it works great! the right front wheel has a lot of camber!

[@Turbochargedtwelve]

You need someone who can print in a material that will cope with heat and fuel exposure. Nylon 6-6 works.

[@22Steez]

@@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

[@Turbochargedtwelve]

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.

[@curtism7203]

@@Turbochargedtwelve Exactly, PETG is better suited for chemicals and heat not to mention its stronger

[@drift_boi2843]

Lol i am not the only one who noticed✋

[@ptolemyp-w]

The flames though.

[@patsguitar5187]

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

[@robinward3003]

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.

[@DocumentaryHub]

For the forth time.... IT NEEDS A GOD DAMN FUEL PUMP!

[@hunter100t]

maybe maybe not, are you sure, you don't sound convinced lol

[@DocumentaryHub]

@Skott at high RPM gravity isn't enough to fill up the carbs. The bike this engine came from has a fuel pump originally.

[@kodykoerselman6758]

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

[@charliewolf7500]

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.

[@jbncnow]

I totally agreee

[@caseybrunson541]

the poor spark plugs are prolly killed with fuel

[@stevemaccollum4688]

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!

[@dirtpro4142]

Front right wheel has a lot more camber then the left

[@drift_boi2843]

I know right 😂???

[@gregmyatt9932]

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.

[@TheGingerJonny]

It sooooo sounds like coils/cdi :) awesome though!! Love your stuff!!

[@mblizzy]

Man that thing is sooo sick! I still can’t believe how awesome this thing came out. Great work boys! By far my favorite build so far. I’d take this over a quad I think.

[@colossebdumont879]

I must say, one of your videos is a very nice birthday present for me ! Turning 16 today !

[@propaneandpropaneaccessori3446]

Enjoy the next two years

[@isaacitllbefine7231]

Happy birthday

[@colossebdumont879]

@@propaneandpropaneaccessori3446 ty man XD

[@colossebdumont879]

@@isaacitllbefine7231 the man himself responded to my comment, well fuck now it's an even better gift !

[@Thisoneguyinaz]

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!

[@feeterican]

Is it me or is the right side front wheel Cambered (bent) out more than the left?

[@marksmithson1414]

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.

[@sunsetsportbikes9435]

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

[@scottwarren1226]

I am an expert butt...

[@ihatejoze]

Man I loved that mad scientist montage!

[@DeliciousDeBlair]

What about valve float? ~( 'w')/ Older springs getting tired and weak might be an issue?

[@MizMods]

Also valve clearances. If it wasn't maintenanced it definitely. Could have valve clearance issues.

[@race-all]

Not reving high enough for valve float.

[@DeliciousDeBlair]

@@race-all That would depend n how weak the springs had gotten, but I do not insist that valve float is the problem. Still, it would be very foolish to simply rule it out.

[@race-all]

Those would be some really weak springs. Possible keepers letting loose pistons making contact with valves. I wouldn't rule it out, just too many other things they haven't checked yet. Seems they have been lucky not to have blown it up one way or another. I like watching how others trouble shoot.

[@Steelythestacker]

I agree Delicious. Sounds like float to me as well.

[@johnnykobra7256]

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!

[@MD-bk7kb]

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?

[@rcplayer7581]

Word

[@Chris-yy7qc]

True. My neighbor is yelling at me because Im watching cars and cameras videos too loud in his opionion. lol

[@rcplayer7581]

I got to fight my neighbor over a rc truck lol

[@rcplayer7581]

I got told my yard not a stadium its a residential neighborhood tired seeing flying rcs out his Windows

[@CarsandCameras]

Hahaha we do have AWESOME neighbors

[@jakeds84]

You guys are awesome. It's so fun watching your KZbin channel channel.

[@Vintageguy73]

Anxiously awaiting next episode!

[@mybackhurts7020]

Mario kart is looking great

[@bbinkley11]

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.

[@bolsen1981]

hey Isaac. 3:40. you missed a hair while shaving :-D

[@MegaKencam]

Been there, done that...

[@LittleMikeStarCraft]

lol saw it too

[@pterodox123]

I like it,,,,,,,,, looks fashionable.

[@devicemechanix9049]

Saw that too. Lol

[@tkskagen]

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

[@djohnson1110]

You are running straight pipes. Zero engine back pressure. Could be several small problems together

[@alt7488]

back pressure is a myth ...just ask uncle tony

[@zethloveless7238]

Al T back pressure on cb750 is not a myth. Try doing homework buddy

[@alt7488]

@@zethloveless7238 lol...well it seems to work on top fuel dragsters ...among other things

[@zethloveless7238]

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

[@alt7488]

@@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

[@eladvanallen8282]

YAAAASSSSS!!!! MORE MORE MORE SLO-MO IKE MONTAGE!!!!!!!!

[@patricktolmie6985]

Hey guys Isaac and whatever try changing the spark plugs NGK racing plugs

[@losi8ightyew]

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.

[@chettharp2532]

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.

[@peytonyoutubee]

C&C: (goes offroad) (doesn’t get stuck) Me: how?

[@safetyboots2642]

As Jeremy Clarkson would say... MORE POWERRR!!!

[@19702260]

Great job guys! High rpm cutout could be low voltage ignition issues. You should sand drag it, im thinking it will pull wheelies with paddle tires.

[@ps3joey6583]

The old carbs are most likely fine they just need bigger main jets there’s to much air not enough fuel

[@shark11175]

Its 2 rich

[@Mustangfleming]

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.

[@stevejacobson2406]

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

[@CarsandCameras]

It'll be fine. We figured it out

[@ProlificInvention]

THIS IS WHY I WATCH!!! Great video guys.

[@jcgoulet4709]

I think you may need more back pressure, try exhaust system. Good Luck!!

[@ChucksCustoms]

Sounds like your points might be floating. Just like valve float, once the rpms go up, things dont like to come back down quick enough

[@glumpy10]

I thought it was pretty obvious it was an ignition issue several vids back. The idea of back pressure is a flawed one. An engine does NOT need back pressure no matter what urban myth says . The idea is illogical. If an engine needed back pressure, performance exhausts would be more restrictive than stock not more free flowing.

[@sweeneysweeney1901]

I like the dual setup. Looks awesome . Lets see where we go from here

[@benmoran6198]

BTW having a muffler increases engine pressure and might help carbs

[@dave1135]

Still need a exhaust and airbox, these engines are tuned for having the correct parts on it. If you start drilling those jets you're going to enter a nightmare world. I had a cb750k in the early 80's, and tried to run it how you were. It wasn't until I bought a junk bike and raided the airbox and exhaust did it finally run great

[@swandonovan]

Remember, I work at eBay's largest used motorcycle parts dealer, MRC cycle, and offered to sponsor you. We've got TONS of engines

[@DeliciousDeBlair]

Are they AFFORDABLE...? ~( ,m,)~

[@rcplayer7581]

You guys buy enginges i have a trx 450

[@mathdebates7936]

Have any 50cc 2 strokes of parts? I'm cooking up something crazy.

[@swandonovan]

@@rcplayer7581 not really

[@swandonovan]

@@mathdebates7936 moped or shifting?

[@Everett-xe3eg]

MAD ISAAC the mad scientist. I love you two

[@moparcasey3135]

I think y’all are on to something with ignition problems.

[@CarsandCameras]

At this point it has to be!

[@moparcasey3135]

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!

[@shark11175]

Amazing editing

[@ronaldseabury734]

It's running on three cylinders you've got a bad coil.

[@Chris-yy7qc]

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...

[@CarsandCameras]

Turns out it was actually running on TWO cylinders at times

[@jgoopra]

@@CarsandCameras ignition module or pulse generator?