A buddy of mine just bought a 1978 CB400 Hawk. We put new set of bars on it and now for some reason, it doesn't want to go above 40mph. Could this possibly be caused by tugging on the throttle cable while swapping it off to get it on the new bars? It seems like a gearing issue, but we never tweaked anything that could have changed that. The engine is revving fine, but when you get it up to 40mph the engine is running like crazy, but it isn't moving as fast as it should be.

 

My guess would be to check the clutch cable

 

try changing gears...