I have a 1981 XS250, the problem is the revs don't drop or drop very slowly when revved. It seems fine when first started but as soon as it starts to warm up the problem starts. I have thoroughly cleaned the carbs twice with air line without success, diaphragms are ok, it has good compression, timing good with good spark at the plugs. I fitted new manifold rubbers and can see no leaks elsewhere. Any suggestions will be much appreciated before I put a light to it.
Cheers