73 Honda CB750 Custom Build Episode 35 - Carburetor Synchronization

This week I build a manometer and synchronize the carburetors.

[@patrickpaakki1584]

Your content is really great i am planning to buy cb750 i was hesitant becouse i knew its Lot of work to keep it in good condition your videos have given me the confidence that i can do it my self. Thanks keep it up💪

[@HackaweekTV]

Go for it!

[@Chopik1149]

Great video. Thanks so much for taking the time to put that together. All makes great sense. Nicely filmed. Excellent commentary. *****

[@iviaverick52]

All the videos you are doing of this project are insanely helpful. I'm looking at starting a custom build on a 79 or 80 sometime this summer (want to find a DOHC engine) and I'll definitely have to refer back to all of your tutorials. Of course the DOHC engine will be different on the inside, but these are all still super helpful!

[@gottowonder7168]

Thanks man you were a huge help. I couldnt find the adjustment screw on my 1976 cb750. Much more helpful then the manual

[@skycarl]

Really good tip tutorial Dino. Thanks as always. Carl

[@TexasSlinger]

Great tutorial!!!! I love my efi triumph. Should the apocalypse come, I'll remember this.

[@francoisboucher3756]

Ton français est parfait !!! Your french is perfect ! tanks you for your tips !

[@built2last31]

damnnn dino you fooled me!!!!!!! i was really upset all day for you i only wish you the best from pennsylvania

[@richie9777]

That engine sounds sweet!

[@jeffersonrodriguesdossanto2579]

Very good to know it was just a prank. Here in Brazil following his project, hoping that everything goes well.

[@arnomaas6452]

very nice tool making and use !

[@TRX450RVlogger]

Great Stuff Dino! I was always Curious how to Synchronize these style Carbs.

[@ronicard]

Nice video, Dino!

[@knikula]

I used the dual glass jar method to sync my gold wing. Fill the jars 1/2 way with oil, and connect them in series with two carbs. Whichever way the oil flows shows the imbalance. Worked pretty good. and only used a couple canning jars and some vinyl tubing. I bought the 5mm vacuum adapters , maybe $25...

[@kevinchamberlain7928]

My gaaad, you're a clever chap!

[@JonathanCalkins]

Aquarium air valves work really well to dampen the gauge as well.

[@AimlessMoto]

Dino, the easiest way to stabilize the needles is to put a petcock or small shut-off valve in-line. Start the bike with the valves wide open, then slowly close them until the needles stabilize. This is actually what most carb sync tools come with when you buy them.

[@SquillyMon]

Im glad that you mentioned the STOCK Airbox at the end of this video...I have found that Individual Air Filters do NOT work very well on the CB750...or at least my 74' seemed to hate the individual filters, No amount of tuning or synchronization would smooth things out with the separate filters. As soon as I re-installed the stock Airbox things smoothed right out. Performance was better, the Synch was easier to obtain and she ran much stronger with the Stock Airbox. Just thought it was funny you mentioned it sort of off the cuff at the end...Possibly not knowing just how important that stock box actually was. I think the separate filters need larger jets to be honest...I didn't have them handy so just went back to the original setup and that setup has proven to be Smooth, Powerful and Reliable over many thousands of miles. 34K and counting...Still going Strong.

[@itvinasi]

That is amazing :) looks great:)

[@LilDoggy]

A wealth of knowledge, thank you

[@RichardHeadGaming]

Nice syncro tool setup.

[@leadpelletinass]

I'm surprised you havent done a compression test by this point. Otherwise the series has been very informative with loads of resources noted. Subbed.

[@ww9l]

I use variable restrictors for controlling air flow like you would find on an aquarium. Get them at the pet store for a couple of bucks for a hand full. Then you can use them to dampen the needle movement. Adjust them down where to where the pulses are tiny. More accurate readings. Great idea using the PVC but they didn't work for you. One thing you might be able to try is to plug the brake lines with JB Weld and drill a small hole to help restrict the air flow which may have the effect you desire without adding anything. Like a #30 drill or 1/32.

[@themistoklesv]

yay you found the bike!!

[@confirmation7]

Hi Dino, fantastic and informative video yet again. Just a thought on this bouncy needle issue. The position of the dampers seems to be important. Here's a "what if" for you. I've no idea if it would make any difference or not, but, what if you were to have a short length of tube from the engine to your plastic damper and then instead of having the gauge directly attached to the damper, run a longer length of tube (about 2 ft.) from the damper with the end of the tube attached to the gauge. Anyhoo, keep up the good work with those videos.

[@Graabein1]

Nice :) I Wish I knew how "simple" it really is to sync carbs when I had my vfr 750 :)

[@MidwestMotoRider]

Wish I had seen this before I paid for the one I have your setup seems to work better and cost way less.. sigh.. Well if these ever go I will do this for sure! Thanks!

[@ZenModLabs]

you need airstream reduction on rubber tubes , to decrease needle jump sort of adjustable clip or vice

[@rockncox]

t'es une machine! good job! ;)

[@gorgon9786]

hahaha.. -"what year is it?".. lovely Dean!..;) -and you really had me running for my pillbox yesterday! ..damn!! I really thought your shits happening...:) -great when you got them all synchro, and the whole engine fell lovley in tune!..

[@brufnus]

Like Paulo wrote, install a limiting jet (adjustable) in the lines; that'll enable you to get rid of the flutter.

[@yekvet1]

Usefull topic, thanks...

[@mrp410]

Nice job - thanks!

[@kensteinke5680]

Great video's and very informative. I have a 1971 Honda CB 750 that needed the head gasket replaced, so I did a top end refurbish including piston rings, hone cylinders, lap values, clutch friction plates, new sprockets and chain, front forks and swing arm removal and regrease and oil, and miscellaneous cleaning and replacing. I have an issue, cylinders 2 + 4 run twice as hot as 1 + 3, as per infrared themometer. 1300°F -700°F. A mechanic friend of mine said that's usually a timing issue but since cylinder 1 + 4 are set at the same timing mark, #1 shouldn't be cold while #4 is hot, and the same with 2+3. with your obvious knowledge what else might I look for? Carburetor jets are all clean, but haven't balanced or synced them with a manometer, only by ear. My local Honda dealer is reluctant to discuss anything older than the year 2000. This bike has only 16,000 miles on it and is totally original even the mufflers. Baffles are snarly though. I had it in storage for 31 years but started riding it again in 2018 because I retired so the head gasket had lots of time to dry out thoroughly. I've watched all of your 41 videos re 1973 Honda cb. This is coming to you from Kelowna BC Canada. Ken.

[@pocoapoco2]

I have an idea to use four MAP sensors and a 5v regulator hooked up to a four channel oscilloscope to do this. My feeling is that all that extra air volume that synch tool adds to the normal operating volume affects the way the thing is going to run. Up to this point I've been synching carb sets without any special tool. All I do is visually sync the slides/throttle plates initially. Then turn the idle screw up to a fast idle like you did but not quite as much. Maybe to 1,500 RPM. Then one by one remove and replace each spark plug cap in turn and note how far the RPM's fall with each cap removed. I have really good success doing this it just takes longer I imagine than with using a specialized tool. One more thing, I think you can get away with adjusting the idle screws with the rpm's above a normal idle when they are air mixture screws, however if they the more common/more modern fuel mixture type the slow circuit (as opposed to the idle circuit) ports begin to become active and you won't get a good adjustment on the screws, so you should adjust them at a normal idle speed. Even though I'm working on bikes like this on a daily basis I do appreciate seeing the level of rebuild you are doing to this bike.

[@stevenlamphear1945]

If you lower the needle the vacuum increases by closes the opening. Opening the gap reduces the vacuum.

[@007mercucio]

My shop manual calls for about 8 psi of vacuum on each carb. The threads on the screw, however, only allowed me to get it into the 5 psi range. At least I managed to get it above the zero it started off at. Come to think of it, I am not sure if the shop manual told me to get that PSI for idling speed or for running speed. I need to go back and check. And, I was having trouble telling whether I should focus on getting a sync at idle speed or at running speed. I went ahead and focused on idling speed, but already I'm feeling reservations about that. I suspect I should optimize the carbs for what they are designed to do, namely to move the bike, not just to make it nice while idling.

[@007mercucio]

Hot glue starts leaking air around 60-80 PSI. I made a crazy contraption with it once... that was where it began leaking...around 60-80 PSI.

[@toms1466]

Good stuff, thanks

[@BanjoRen]

Hi Dino, don't know if anyone else mentioned this but the reason the pipe didn't dampen the needle fluctuations is due to the vacuum being created. There would be no air in the pipe, (vacuum remember?) therefore nothing to dampen the fluctuations. Great build though, cheap way to make a manometer. Looking forward to the rest of the build and future hacks.

[@BasicPoke]

There is air in the pipes, just at a pressure a little below the surrounding air pressure.

[@bradhawdon6203]

Your awesome . Just doing up some cb750 carbs . You saved me alot of fn around . Big loves from OZ

[@HackaweekTV]

Rock on!

[@alexansouza]

Very nice

[@TC-gn2by]

A little grease under the carb throttle cam follower is good

[@williamfernsndes6409]

este é o cara!

[@stevenlamphear1945]

Another way to dampen those pulses is to fold the hose and clamp it with a clothes pin. Adjust it so it's a bit slack.

[@Ramekenas]

what if you pour oil into the gauges? like they do with all of them :p that should dampen the wobble quite a bit

[@nightflyer1100]

Piston engine airplanes have same device call MAP gauge. Manihold Air Pressure.

[@clintharris94]

So do you screw your vacuum port screw all the way back in after you're done sinking

[@scottchartrand2322]

I've got a 75 cb750f that is running a little too lean, pod air filters on all carb inlets and no muffler. What size main jet would you recommend?

[@rjlindner757]

I have a 1976 honda 750 that my grandfather bought new an then my father bought off him now it is in my possession. I cleaned the bottom end of the carbs and tried to start the bike after changing spark plugs and oil/ oil filter. I'm not getting fuel to the outside two carbs any idea why? I would assume it has something to do with the carbs or a clogged line I'm going to check that now if it's not that I would assume it's something inside those two carbs clogged up. do you or anyone else here have any guesses of why those two are not getting fuel?

[@daveco1270]

Does adjusting the airscrews have any affect on the manometer readings? I'm assuming it doesn't. Getting those air screwed dialed in perfectly has been tough on my CB750. People talk about the idle drop method, but mine don't seem to have a huge effect on the idle, at least not that I can see on my stock tachometer...it's very subtle shifts. I try to set them so it's running good with minimal popping on deceleration, which isn't always the exact setting for the highest idle.

[@dinomejia9224]

GREAT A 1OOO THN´X

[@andrewshutty3345]

no primer with glue on air tight? luv you bro

[@Kostghost001]

Using manometer to synchronize carburetors is a good idea. But we prefer to use medical dropper and some kind of oil. This is much cheaper

[@StanleyKubick1]

+Даниил Комаров that sounds cool, is there a video?

[@DoogieLabs]

I feel like if you went with a really small orifices into the vac chambers that combination would dampen the readings enough. Question: what is the appropriate head temperature operating range for an air cooled bike? . Thanks for sharing.

[@SeanBZA]

+Doogie Rick Puting some smaaler tubing into those lines would do the trick, probably around 5 inches of 4mm tube pushed into the end on the damper, and then this will do damping better. Otherwise a small inline fuel filter per line also does a good damping job, as it restricts flow. Of course you can use inline needle valving to do the same, but then you need to set up all 4 at the same level, but the speed control fittings with integrated needle valves are cheap enough, just put in and tighten all to full then back off a turn.

[@CraftwerksMC]

Like others, still upset about the AFD joke but its all good, lol. Dino, FWIW, using a liquid setup offers some stability to the reading because the liquid doesn't allow the vacuum pulses to jump the gauges around nearly so much. You can probably get it in the ballpark with the gauge setup you have but it'll be easier to completely balance them with a liquid based setup.

[@gixerman01]

nice, but wouldn't have been easier to buy a mercury stick?

[@hammershigh]

Shouldn't the ignition timing have been verified first? And maybe also pressure tested the manometers. An idea for an electronic device: with an arduino with pressure sensors, it would be easy to make the damping/filtering in software :) Good video br

[@sidepipechris1]

did you set the base idle with the throttle adjustment on the thrrotle cable or the individual rods on the carbs?

[@HackaweekTV]

Initially the cable.

[@Doc_89]

What would happen if you use liquid filled manometers? Will there be a different (bad) reading if you eliminate the fluctuation?

[@DeanSegovis]

+Doc They don't jump around as much.

[@SuperPoonSlayer]

Hi, can anyone help me with my 1977 k7 cb? the carb you're working on has the adjuster screws outside the throttle needle house whereas mine is inside. to adjust, do i take off the 2 screws while the engine is running? will that affect the manometer reading, vaccum, etc...?

[@krabkrabkrab]

Yes, it runs fun with the carb top covers off.

[@nuktan]

Manometro mastora..

[@remobigelow7821]

Are thoes the original carbs for this bike I have an 84 CB 750with completely diff carbs and I am having a heck of a time trying to run it without the stock airbox I've done everything I know how too diff jets, tapeing the aircleaners, and diff plugs and timing

[@remobigelow7821]

Anyone know any carb sets that will work with air pods and with a 1984 Honda CB 750c ?

[@arkangel13th]

man-o-met-tr-heu :) I'm french canadian,yep :)

[@marvinjobs2570]

👌

[@puffintyler7868]

Hey Deano, could you explain what you did with the idle screw adjustments after you did the carb sync? Thanks

[@DeanSegovis]

+Puffin Tyler I turned them in to see where the idle dropped off. Each one slowed down at 1/2 turn so that tells me two things. One, the idle circuit is flowing fuel, two, turning them back out to one full turn smoothed the idle out. I set them all at i\1/2 turn out from the point at which they caused the idle to just start to slow down.

[@puffintyler7868]

+Dean Segovis Thanks Dean... appreciate the response and love the videos.

[@drumstyx]

What'd the whole gauge deal cost you? I just paid $125 (CANADIAN) for the Morgan Carbtune, and it's way, WAY superior to dial gauges. I have a set of the dials too, but I just finally wanted something decent.

[@JRWperformance]

you can get rid of that gauge flutter with air restrictions. I used old carb jets in the tubing. The smaller the jet the better.

[@DeanSegovis]

+JRWperformance Aha!! Thanks!

[@painchaudd]

+Dean Segovis this was exactly what I was going to recommend. Shove some old main jets in to your tubes and that should quiet the needles up. I have ordered some gauges to build the same setup. Thanks for the inspiration Dino!

[@fjanssenBe]

hi, did you use standard size jets (with the pods)? thx! great series!!

[@DeanSegovis]

+Fred Janssen Standard size jets but the pods are not going to be on the final assembly. I'll be using the stock air box.

[@fjanssenBe]

+Dean Segovis, i guess i'll watch the next video until the very end :) where you say that you won't be using the pods :)

[@joelcr250]

*Im still mad about the april fools joke*

[@TRX450RVlogger]

+CR2504life I see you comenting everywhere lol

[@rickyrobinson3096]

The 4 hoses on bottom of carburetors...where do they go? 1974 CB 750

[@HackaweekTV]

They just hang down below the bottom of the engine. They are for draining the float bowls.

[@rickyrobinson3096]

@@HackaweekTV Hey Dean quick question I have the 74 CB750 the bike starts up first time every time with a Kickstart because the battery is completely dead throttle is real responsive only problem is is it dies unless it's throttled any advice? Everything on the bike is stock just replace the plugs put new Jets in the carburetors just can't seem to figure it out I can't keep it idling

[@sarathai2876]

Your Manometer works but it may work better if you place some resistance between the gauge and pvc tube. Like to start a .010 dia hole or a small fish tank air line valve. Air is just too fluid to just screw a full open vaccum gauge in a tube.

[@DeanSegovis]

+Sara Thai Agree. :)

[@muh1h1]

Maybe should have tried putting rags or whool into the chaimbers, works for sound dampaning too :)

[@StanleyKubick1]

+muh1h1 that would just take up air space better used for dampening

[@muh1h1]

Ace Futura well, bascally what is causing the needle to vibrate is rappidly changing pressure => Sound. Sound is dapmened by whool or rags, because it is absorbed. it may not have worked that well, but it would be worth a try.

[@StanleyKubick1]

muh1h1 sure, worth a shot

[@anthony_sasquatch8056]

Crafty/smart guy haha

[@frazbmw]

If you were my neighbor, I would lobby to become your best friend.

[@Gulgonful]

Man o meter

[@krabkrabkrab]

I still have my mercury carbstix. Anybody want them?

[@brufnus]

Are those the floating ball type?

[@novachannel1981]

jb kwik is the shit man

[@jeffhendrix665]

I have made a electronic manometer that you would use with a 4 channel scope. made if from 4 map sensors and a 5 volt regulator. I have also made some modifications to your fuel injector tester that you made a few years ago. I would like to be able to contact you but cant find an email.

[@DeanSegovis]

+jeff hendrix facebook.com/HackAWeek/

[@thegenerousdegenerate9395]

Wait... What? It's not stolen? It really was an April fools gag? YOUR EVIL!!!

[@klannstyle]

haha, did somebody clicked on snoopavision and saw the message at top? It sais: "SnoopaVision is in beta and will be enabled on 73 Honda CB750 Custom Build Episode 35 - Carburetor Synchronization by 12/16/2103." That means beta till then? ... just fun fact, no offence to anybody. There are so many years till this one will go there. :-) (posted on apr4, 2016)

[@Questioneverythingg730]

Great video thanx. I think they use metal rods now in replacement of mercury. I have the carbtune synchroniser. Excellent bit of kit and extremely stable and cheap. www.carbtune.co.uk/

[@farhatkhalid6713]

Ok lik

[@Rodney5822]

How do you sync carburetors in the sense of air/fuel mixture? Do you go by sound? Thanks in advance!

[@truantray]

Just feel it on test rides, or use a color tune

[@Rodney5822]

+truantray That's what I thought thanks!

[@farhatkhalid6713]

Cb 65o

[@minhthaole3587]

ONG NOI TUI KO HIEU NHUNG THAY CANH LAM THI TUI RAT HAY TUI CUNG MOT THO MAY

[@jamesstepsidechevy]

first.

[@Graabein1]

Nice :) I Wish I knew how "simple" it really is to sync carbs when I had my vfr 750 :)