I have a really nice restored XS250C. It runs OK but when throttle is closed the engine revs drop slowly which makes changing gear etc interesting !! Idle speed is set to 1200rpm but it only holds that when its hot i.e. after a good run. Everything looks OK, ignition is set up right, - plugs are OK, running slightly rich on both cylinders perhaps but not too much. Is there anything simple to check out. I'm considering a full carb strip but am unsure what to actually check. Carb butterflies snap shut when the throttle is released so is there something else? Do the carbs need synchronising. I'd appreciate any help / advice !!

It could be two things. Air is being sucked in via the butterfly spindles or the mounting gasket. Secondly, the air valve for the main jet or the diaphragm, I don't know which type of carb you have, is leaking.

If you stop the air getting in after the petrol, you are on a winner.

to theforum wtf61!

try a little oetrol additive as I think the carbs are displaying a blocked pilot hole at the top front of the carb. this tends to hang the revs. it usually gets worse when hot!!

have a look at the sticky at the top of this section as there are some usefull links for you to try.

drewps