high speed miss

[Mike Reaves]

I read a few years ago about this miss on thumpers and now it's come up here as well. As I remember there is a point (rpm) when the intake valves close and the reflected pressure wave in the intake tract will 'push' the charge back toward the carb. On the next intake cycle the valves won't be open long enough to re-accelerate the intake charge before the valves close again in effect starving the engine for that cycle (causing the miss). As I remember it's a function of tract lenght, carb size, rpm and tract diameter. I think mine happens around 4500-4700 rpm (70mph). Anything faster or slower the machine runs great, but right there on level ground and steady throttle I can feel this miss.