Motorcycle Carburetor Bench Sync

[@LegitRaceCraft]

usually you only resync them if they are running rough. You can do it this way instead of using a manometer, but the manometer is more accurate. This way gives you probably 90 - 95% the accuracy compared to using the manometer. It will work regardless of whether you are running the stock jets or larger ones.

[@LegitRaceCraft]

The fuel economy problems in carbureted bikes almost always lies in the spark or the carburetors. You should check your spark gap first on your spark plugs and if your coils are still providing a hot spark (resistance check on the coils, the repair manual describes how to do this). That is the easiest thing to begin with and rule out. Then clean the carburetors well. If done correctly it should run great after that.

[@alwaysasoldier2708]

used your video to do the carbs on my bike. Bike runs great now! A++

[@LegitRaceCraft]

It is the high-E string from a guitar, the smallest string. If your carburetors are in sync then it may help your mileage if that is the problem. Your jets could be a little clogged, air/fuel screw not adjusted properly, or a ton of other things. Even spark plugs or ignition coils.

[@BLASTERGIFT]

ive synchronized my carbs in just two minutes with your help.Thanks

[@fleuroman]

Interesting method Jay, I'm guessing it wouldn't matter what size steel string you use so long as all 4 butterflies are opening the same distance at the same time but the smaller the better, the only way a manometer would be more accurate is that method allows for variations in compression which is what really controls the amount of air going through the venturi.

[@mattmiles8895]

Great vid thank you

[@chrisliddle2236]

Thank you so much I did this and worked a treat did it all and started bike and could bring down idle before I started to balance cheers 🥂

[@LegitRaceCraft]

I would look to see if you have an air leak between the carbs and the engine. Maybe one of the manifold boots has a small crack in it and is letting more air in on that one cylinder. Then the carb is matching that air with fuel and the engine ignites the mix. This is just speculation, but it is where I would look. I know mine had a couple manifold boots that were dry rotting. Other than that, I have no idea. Maybe a thorough carb clean?

[@HoustonR6ryda]

So a bench sync is a must after I disassemble the carbs for cleaning?....to get it to start for a true manometer tune?

[@LegitRaceCraft]

If you fully disassemble them then you will need a bench sync for sure. If you just disassemble them enough to clean them you don't need to sync them unless you want to (I would though). You can get them fairly well balanced with a bench sync, to where they are about 90%-95% balanced, or use a manometer to sync them to 100%. If they are bench synced properly they run very smooth

[@huimotorco]

Just curious if you have a video or advice on how to bench sync mechanical slide carbs?? Mine are Keihin PD50a style and the butterflies only seemed to be controlled by the choke, the slide itself is controlled by the throttle...any help appreciated!

[@jamesparker9174]

How linkages sync chokes & idle ajustment

[@jamesparker9174]

Linkages Jaming apear upside down / screwed up

[@LegitRaceCraft]

On my other carburetor videos I have quick links on the left side to help people jump around the video to certain sections. I must have never put them on this one, and just thought that I did. I didn't realize it until you said something, so thanks. Check out the other videos to see what I'm talking about. I get about a subscriber a day. More would be nice, but I don't see a large number of views when I initially post a video, so it isn't that much of a concern.

[@lil_grip2384]

Longshot since video is so old, but, what carbs are these off of? Looks like a bandit.

[@LegitRaceCraft]

FZR600 I believe. there are only 3 main manufacturers for the carb sets that came on motorcycles, Keihin, CVK, and I forget the 3rd one. Most look the same

[@lil_grip2384]

@@LegitRaceCraft Mikuni I think. So do you remember ur float height measurements? I’m about to rewatch video in case you stated it I can’t remember.

[@lil_grip2384]

@@LegitRaceCraft just skimmed through ur fzr600 rebuild video, sadly the carbs are much different. :,( great detail in ur videos tho 👍🏼

[@LegitRaceCraft]

@@lil_grip2384 unfortunately I don't remember what the float height is for these

[@harrybanis9898]

This is a good vid thanks for explaining

[@victorperezyproo6557]

Perdón por molestar, me puede mostrar ¿Cuáles son las spreas de aire y cuáles son las de gasolina?????? tengo problemas con mis carburadores y no se a quién preguntar. Gracias ( Son iguales a los de usted Mikuni Moto Suzuki 550cc 1980

[@LegitRaceCraft]

I had an f2 that did the same thing. It was from extra gas exploding in the engine when it wasn't needed after letting off the throttle. The engine is still sucking in a little air after letting off the throttle and the carburetors are mechanical and they are matching that air with a little fuel. The spark plugs then ignite the fuel/air mix in the engine making a pop. It is just extra fuel that has made it into the engine and it being ignited. Mine always did it and it was annoying.

[@briansteele4147]

Hournine Racecraft, carbs running rich. too big a jet size or not enough air

[@sabrom]

if you just pull the bowls on all 4 carbs to clean do they need to be resynched?

[@LegitRaceCraft]

if you are just pulling the bowls off to clean them then you shouldn't have to re-sync them. If they run really rough then you should.

[@jusbrothersmohamed1704]

I will try this method

[@simio312]

would you happen to now why whenever i downshift on my f2 or let go of the gas you can hear some popping or backfire? thanks.

[@D.blevins10]

I have a 94 cbr 900rr I just took the carbs off and the springs for the flaps to open only had 1 I added the other to and now they all open the same. So how can I sync them to be able to ride it till I can have it done right.

[@LegitRaceCraft]

+David Blevins use a feeler gauge if you don't have a manometer..then you can set the flaps open to the same gap. After they are on adjust the main idle screw and that's it. Then set your idle/air control screws to factory specs if you want it even better

[@rockzdan001]

i have honda CB4 400cc super four. can you tel me the jet size of the carbrator? slow jet and high jet? thanks

[@untonyto]

I have the same! did you find an answer?

[@twopax17]

If i sync them using this method, will I soon need to use a manometer? Also, will this method work if you have just rejet your carbs?

[@jr.fiebre3590]

yes it'll be really accurate not 100% but pretty damn good

[@joshk7928]

Good video. I have a 1993 fzr600 and am only getting about 27 mpg or 147km before I need to switch to reserve. This if far below on fuel economy for this bike. Would you know any solutions, cheers in advance :)

[@jamesparker9174]

Slide tied back no spring butterfly fully open jammed up linkages Helter scelter

[@joshk7928]

What chord guitar string is that you're using? If i sync my carbs according to your vid, would I get normal mileage then?

[@TonyNapoli]

High E string

[@simio312]

yea it is annoying! anyway to fix that?

[@Mr_Ashley]

What note and string gauge are you using lol

[@LegitRaceCraft]

It's the High E string, usually 10 gauge works

[@Mr_Ashley]

HourNine Racecraft haha brilliant! Thanks for the reply. Guitar is due a string change at the same time I’m currently have issues for my carbs. However changing stings is easier than pulling the carbs out again 😭. Glad I found your video 👍👍

[@CorySchneiderOfficial]

Nice video, but if you're looking for subscribers, you should probably write up a rough script and redo it in a more concise way. Thanks, though, you taught me a lot!

[@jeffbaker4364]

as long as there all the same its fine,but dont use a broom stick

[@MissShaftable]

Air cutoff valves maybe

[@modikee56inchkeegandafterw13]

what if the valve is weak and other has strong suction? then your wire theory fails...its the suction you are actually synchronizing not the butterfly..i hope you got my point...so vacuum suction gives you some accurate idea rather than yours...

[@LegitRaceCraft]

Thank you for the comment. I understand completely, but not everyone will have a manometer to use to synchronize the carbs, which is the main reason for this method. Separately, the difference of suction between cylinders normally isn't great enough to show any noticable difference while running, at least anything you can feel in the vibration while riding the motorcycle. The difference in vibration alone after riding every motorcycle that I've synchronized this way is enormous after I'm done compared to the rough idle before. It's perfectly smooth after and that shows a healthy engine where all cylinders have a similar amount of air/fuel when they combust. What you're describing is doesn't happen often. When the vacuum difference between cylinders is large enough to cause a noticable difference is also when you would have larger problems. The cylinder with lesser vacuum would cause an imbalance of the air/fuel mix between all cylinders and would still keep the engine from running smoothly since one cylinder would be sucking in a lesser amount of air/fuel compared to others. Whether you use a manometer and make the vacuum as precise as possible or whether you use a feeler gauge on the butterfly valves will make no difference. You would have to fix the valve or whatever else is causing the compression leak and then use the manometer.

[@modikee56inchkeegandafterw13]

i got suzuki bandit 250...and i first did same method you did...but in my bike when i put more throttle in any gear the sound becomes squeezed (not smooth like in one smooth sound like sports)..it becomes like brum brum brum at normal throttle rpm of 3000..so whenever i reach about 3000 rpm i have to change the gear to get smooth sound like in one tone like hhmmmmmmmmmm.........i have tested your method but this smooth sound still not achieving..i also have checked the air fuel mixture setting all are company stetted. now im thinking may be i need vacuum sync...what you think abt this issue...

[@LegitRaceCraft]

I'm having trouble visualizing your sound effects from the text, so it's hard to answer. Have you cleaned the carburetors or just synced them? What was the condition of the diaphragms in the carbs? I've seen creased diaphragms before and that caused some weird issues at certain throttle points. Has this been jetted before or is it still stock? What's the condition of the air filter? These can all affect throttle as well as many other things

[@modikee56inchkeegandafterw13]

ok friend thanks for reply...ill make video for you...yes carburetors have been cleaned and diaphragms are also fine..i got stock jets...air filter also new..i will make video for you..when bike starts in standing position its working fine but only start giving wearied sound when running in gear...

[@elmeyshmey6098]

use a flashlight

[@haylepilotgigclub7983]

oh,carbs like to b smooth,scratching around with a screwdriver and bits of wire,no thanks,check for marks and smooth out don't scratch around,clean and adjust

[@LegitRaceCraft]

It's perfectly smooth wire on the sides, if the tip did scratch it there would be a very minute almost immeasurable mark. I'm not forcing it in and out like a barbarian creating 50 million scratches, I swirl it around the smooth side of the wire. They sync perfectly. Do it a harder/slower way if you like, but this works perfectly every time with no issues. At the risk of sounding rude, don't diss it unless you have definitive proof that one tiny scratch will make a measurable difference in performance

[@blk77ta]

mad at yourself at 4:34

[@mikec4772]

the reason you use a manometer is because not every cylinder will pull the same vacuum depending on wear ,valve adjustment and carbon buildup . that is why you balance with actual vacuum readings . you are giving bogus information . bench setting is ONLY for getting in the ball park so when you re install carbs bike will actually run half way decent . stop spreading BOGUS in accurate information . and just so YOU know adjusting throttle blades doesn't affect fuel intake at all and air fuel adjustment is for IDLE ONLY ! ! ! pilot circuit you make me mad ...

[@Community-Action]

Well said Mike

[@lorenhusky2717]

mike c I agree. This is the way to get your carbs in the ball park. It's NOT a replacement for using a manometer though.

[@charlesfranks5250]

I have a 96 600r model zx600c.any idea where the vacuum lines go.

[@charlesfranks5250]

I have a 96 600r model zx600c.any idea where the vacuum lines go.

[@charlesfranks5250]

I have a 96 600r model zx600c.any idea where the vacuum lines go.

[@jarbello24]

You keep jumping from one thing to the other without explaining the first thing. Try again, maybe knowing what you need to say before you start again.

[@bungcheese5901]

Jason Arbello at first I agreed with you but then double checked, nowhere does it say this is a how to. This is a video of him documenting how he did it. Nothing more