I have owned an ETZ300 fitted with a 301 barrel and piston for over a year now,and love it to bits,apart from one annoying characteristic.This is uneven running on the overun and when running at small throttle openings.The jumping and jerking on the overun I have fixed by setting the carb so that engine just about stops when the throttle is closed.I just have to remember to maintain the tickover with the throttle.
The engine runs perfectly when pulling,but jumps and jerks when cruising at small throttle openings.It is at its worst at about 40mph in 5th gear [about 3000rpm] on a flat road.Changing down makes it worse because the engine is under even less load.I have de coked,advanced,retarded the ignition,weakened,richened the mixture but it is always the same.Is this a characteristic of the ETZ? perhaps an experienced MZedder can advise.