I've got a stock Mikuni 42 0n my 04 Deuce it will run ok off the line but when I get to a high speed it seams like I have a governor on it. It just flattens out. Is it a carb problem? Thanks any ideas? Thanks again.

 

Lean or partially clogged Main Jet?

 

Maybe I'll look how about a pin hole in the diaphragm on the vacuum piston

 

Mikuni's have a mechanical slide, not operated by vaccuum like CV's.

 

OK thank you for your help

 

Maybe you meant it has a stock Keihin C.V. carb and I misunderstood. If it is a C.V. carb it's a Kehin, not Mikuni. And yes, a tear in the diaphragm or if the diaphragm isn't seated correctly, could definitely cause this issue!

http://www.johnsmotorcycleparts.com/...tor-images.htm

 

I might have mislead you myself thanks again I'll look into it

 

To make sure that the diaphragm stays put while I put the top back on I use a little gasgacinch or rubber cement.

 

Thanks great idea