SOHC.co.uk Forums > CB350/400
Carb sync
kevski:
--- Quote from: K2-K6 on December 14, 2016, 08:40:57 PM ---I don't have a reference for the tolerance on these smaller fours, but the 750 is given as 40mm (1.6 in) Hg.
--- End quote ---
I think there is a parameter of 2hg on the smaller fours, around the 22 mark, but it can be any number as long as the difference between carbs does not go out of the 2hg parameter, the air boxes and filters should be left on.
gtmdriver:
I had them off the bike for servicing so I synched them on the bench using a 3mm drill under the throttle slide on the engine side of the carbs When I fitted them and fired the bike up with the vac gauges connected only one of them needed a minor tweak for them all to be spot on.
Don't forget that balancing the carbs is the last thing you do after setting the ignition timing and the valve clearances. If either of these are out you won't get them to synch correctly.
royhall:
It does say in the official Honda manual to remove the air intake housing before syncing. Haynes and Clymer don't mention this. Honda book states 3hg tolerance. Have been through the rest of the settings first but I think I will go through them all again just to be sure. Raising pressure on one cylinder is dropping the other three quite a lot, more than I would have expected.
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kevski:
I find that odd as the air box stabilizes air flow to the carbs, maybe try without the filter at least then there is less resistance.
royhall:
I agree Kev........ I would have thought syncing should be done as near to real operating conditions as possible. Thats really why I started this thread to try to find out how the pro's do it. This is the first time I have done this on the smallest four so need to ensure I am doing it the best way........ On the 750, airbox on or off doesn't appear to make any difference in the syncing (set them up with the filter and lower airbox off then rechecked with them back on)......Maybe due to the small size of the carbs I am making too big an alteration at one go. I will leave it for today and see what the replies bring. Thanks all.
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