After solving one problem with a 376 carb on my M21 a new one has developed. Every so often the bike will not rev up and i found the needle valve was sticking in the closed position in the float chamber. Why would this suddenly happen? Does anyone know of a cure?
Is it bent or not sitting correctly in its clip?
Check the needle seat for wear or minor ridging, try a new float needle, one of the viton tipped aluminium bodied ones.
I take it that you are referring to monobloc carb. If so this happened to my Shooting Star. In the end I cured the problem by changing the float needle seat. I can only think that this wears with the needle rubbing the side increasing the clearance until the needle tilts and jams.