SOHC.co.uk Forums > CB350/400

More carb troubles, engine won't return to idle revs

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Nurse Julie:
Bill, I'm down in Crowborough from Wed 23rd November for 5 days. If you haven't made any progress, I don't mind coming over and collecting the carbs, bringing them back to Lincs to check them out for you. But, by what you have checked already, I would really only be going over everything again.

Nurse Julie:
Just a thought Bill, did you fit the carb to manifold stubs in the correct orientation?  If yours are OEM, if they are fitted correctly, they should read 1,2,3,4 from left to right whilst sitting on bike. The 2 middle ones, 2 & 3 are angled differently than 1 & 4, if not fitted correctly, air may be getting in.

billdn:

--- Quote from: Sesman on November 13, 2022, 04:14:35 PM ---If the throttles are snapping fully closed, which is very easy to prove, I’d not somebody else’s pension it’s a pilot jet/pilot jet route partial blockage.

--- End quote ---
I'm taking them off ...again so I'll have a check but all were cleaned before reassembly but you never know 👍

billdn:

--- Quote from: Nurse Julie on November 13, 2022, 05:13:47 PM ---Just a thought Bill, did you fit the carb to manifold stubs in the correct orientation?  If yours are OEM, if they are fitted correctly, they should read 1,2,3,4 from left to right whilst sitting on bike. The 2 middle ones, 2 & 3 are angled differently than 1 & 4, if not fitted correctly, air may be getting in.

--- End quote ---
I do remember checking that as they have a number embossed on them I recall.  Have tried spraying them when running with carb cleaner and no pick up in revs. Thanks for the offer Julie, I'll persist in the meantime but if without success, may well take you up on your offer. 👍

Scottish Badger:
I've just finished rebuilding a spare set of carbs on the bench, here's my thoughts based on what I found whilst setting them up "static".
If you don't screw all the linkage balancing adjusters in far enough, the throttle slides can be held ever so slightly open.  Also, the butterfly stop bolt can be set wrong and prevent the carbs closing off fully - with the throttle fully closed there should be a gap between the butterfly and the eccentric stop pin.
Having said that, revs hanging up on closing the throttle used to be a classic symptom of an inlet air leak somewhere....  but if you're convinced there are no leaks, I'd try screwing the balance adjusters all in by the same amount, say two complete turns? You may have to readjust the fully-open throttle stop afterwards, to achieve full throttle, without the slides rising up beyond the carb bores. Hope this is of some help.....

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