SOHC.co.uk Forums > CB500/550
Carb sync question
DomP:
I'll probably test my patience refitting the carbs tomorrow and see how it idles, hopefully an improvement on how it was, no3 carb float was at 23mm rather than 22 so that may have had something to do with it
Laverda Dave:
I am losing my patience setting up my 400/4 carbs. They have now been off the bike three times. I have been using a 1.5mm drill to set the slides (from the engine side). I put the carbs back on the bike and one of two things happen, it will either rev it's nuts off at 300rpm (throttle stop wound fully out as is the fast idle screw), OR it won't tick over at all and if it does it runs like a pig and the vac gauges are miles out between the carbs even though they have been bench synced!
I'll take them off again tomorrow as something is obviously wrong somewhere but I cannot find what it is or are my carbs just worn out?
McCabe-Thiele (Ted):
I would try either 1 mm or go for the point where the lifter just starts to rise.
I used this as a guide https://www.vintagebikebuilder.com/cb350-400f-carb-rebuild-demonstration.html
I did not have a 1/8" drill bit as per the vintage bike builder guide so went smaller I think it was 3/32" but not 100% sure it might have been a tad smaller.
If you go for the point where the sliders just start to rise on each carb you could then check if there is enough travel in the
throttle stop screw for it to adjust up to 1/8.
Bryanj:
1/8 is a bit big 1mm far better.
I back off the adjuster till the slides bottom then slowly open it till the drill just fits under one slide and adjust the others to suit
DomP:
--- Quote from: Bryanj on July 21, 2024, 08:34:11 AM ---1/8 is a bit big 1mm far better.
I back off the adjuster till the slides bottom then slowly open it till the drill just fits under one slide and adjust the others to suit
--- End quote ---
That was my mistake, not using the idle to open them up to take the 1mm bit before adjusting all to suit. I think I've got them right now, idle screw is nicely in the middle of its range and the throttle stop screws will adjust to meet.
*The only thing I've noticed is I seem to have too many threads showing on the adjusters, 4-5
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