To sync or not to sync??!!
 

Hey ladies and gents, thanks to this valuable resource, and the great advice, I got my 96 600F3 carbs back together. Got some OEM jets from jets r us and all is well. my question now is, do I need to sync the carbs? the engine was running fine prior to disassembly. I took them apart for what turned out to be a vacuum leak, and decided to tune up the whole shebang!! SO... any help is much appreciated. Is syncing necessary? if so, is a bench sync possible and how do I do it? As always your time is much appreciated and thanks in advance.

A bench sync is where you would "twist open the butterflys with your hand" acting as throttle cable, so all 4 are open. Then put a for example a 1/8 inch drill bit in the main carb to hold the butterflys open. Then use another 1/8 inch drill bit as a feeler guage on the other 3. Adjusting as necessary. A bench sync would get you in the ballpark if they were way off. But a proper sync with the carbs on the bike while running would dial it in perfectly. I doubt they were way off if the bike was running pretty good in the first place. A sync is based on the amount of suction each cylinder is pulling. Each cylinder could be sucking differently based on the amount of wear so a bench sync could be way off. So a proper sync with the engine running and the sync tool hooked up is the best way to go.

How well could the bike been running before with a vacuum leak?

Do it right and sync it properly.

Thanks CMF. good to hear from ya as always. Such knowledge!!!! LOL @ 74. A valid question. It was a situation where it was running perfectly, and then it died on me at a stop sign. I F'd around with it and got it fired up again just to die again 2 miles later. Got it running again and got it home thinking it was starved for fuel and said "hey Ill tune this bee-otch up while im feeling froggy". Pulled the tank and found a hose with dry rotted end had come completely off the shifter side solenoid filter assembly. So it was a massive and blatant vacuum leak, and it was running great up to the point. Advice taken on the sync. Ill make it happen. i reckon a sync tool wouldn't be a bad investment. Any leads on where to get a good one at a reasonable price, and any other accessories and or advice ill need? much appreciated

If you really, really want to go all the way, check your valves prior to syncing the carbs. Insuring they are within tolerances helps in knowing you are good to go.

these gauges work great, just make sure you use the small valves, and calibrate every gauge on one cylinder before you sync them all.
New Vacuum Carburetor Synchronizer Carb Sync Gauge GL 1100 1200 1500 Honda CB | eBay

oh and the brass tubes are meant to be used on older hondas so dont bother with them.

+1 on those guages. I own a set and love them.

Thanks sj. do they come with tubing? i know it wont be hard to get if not. Also, would you mind to elaborate on calibrating to one cylinder? I cant wrap my head around how it would be a known value? what is the vacuum measured in? water column? microns hg? thanks in advance. Ill probably have more questions as this will be my first time

Thanks for your input too ham. Im scared to get into the valves though if I dont have too

Your #3 cylinder is used as the base. It doesn't really matter where its position is. You aren't trying to get the other three to a certain value. Rather, you are striving to get all four cylinders to have the same vale. To your question concerning the what is used, a variety of things can be used. Some people use ones with liquid. The ones sj recommended are gauges. The basic premise is get the need on each of the gauges to have the same value able move exactly the same way when the bike is idling under a warm engine. The particular value the needles show does not matter.
The reason you use #3 as your master is because once you achieved a proper sync, you use the throttle stop screw on #3 to adjust you idle rpm value to where it should be.