ORIGINAL: Flyboy Dave
....The "timing" has to do with the port timing. That is to say....the ports cut into the
cylinder liner. The port cut into the crankshaft, under the carb mount has nothing
really to do with the ultimate rpm of the engine., as long as it is not restrictive.
FBD.
A crankshaft port that closes early will restrict the top RPM's of a engine that is otherwise timed to really spin up. My skyward .40 (picco) is a good example of a engine that was tamed this way for "sport" use.