I have just completed a top end rebuild on a 1970 CL 175. Last run in 1988. The problem I have is the motor is breaking down under high revs. It starts easily and runs fine up to 50kph, any faster and revs over 4K it stutters badly and wont rev out, like it is running lean but the plugs show ok, maybe a little rich. I have lifted the main jet needles one notch which seemed to improve a bit. Installed a new carb kit and have tested for manifold leaks. I am at a dead end with this now. Anyone had this issue?