The hole in the jet can be blocked with gunk. The seal on the Prima cap can be rooted. And the diaphragm can be mangled.
holes/cracks in the float. The needle can be excessively worn. And cracks and fractures in the body of the whole carby in general.
Also, there is lettering (A, B, C) on the head of the puppet valve. Which the work shop manual talks about.
Sometimes depending on which letter you have lined up with the groove in the seat where the valve sits it can affect the revving of the engine.
That's what I've found anyway.
