vespa pk50

[markdoyle]

spence thanks for helping. as i said my son is having problems with a racing engine. i have replaced the throttle cable because it had a kink in it, still didnt solve the racing was advised spring on carb needed replacing replaced that solved for a short time. the pk is used every day starts first time very reliable but every now and then when coming down through the gears the engine races mainly in 1st gear let the clutch out engine stops racing over the last few weeks hasnt done it as much due to turning revs down just cant understand why it does every now and then.could the problem be the carb slide or do you think it may be something else because i am puzzled

[Smallframe]

Sounds like a worn carb, or an air leak on the manifold. I assume its a standard carb. Have you tried turning the mixture screw to richen up th mixture. Does this only happen wghen engine at full running temperature. Try a few trial runs with different air screw settings as that was the cure on my brothers et3.