If the mechanical advance slots and pins are worn, and the combination of the mechanical, vacuum, and static timing fail to reach the maximum advance, the motor quits performing at what ever rpm level the reduced advance can obtain. Everything will work perfectly up to the point the timing can no longer advance. Total timing advance in the 20-25 degree range will limit the rpm the motor can reach, but it can run wonderfully up to that point. This would be an ignition issue.

There can also be a fuel pump that can not deliver the full amount (volume, not pressure) of fuel the motor needs, the rpm range will also be limited. It too can run wonderfully right up to the point there isn't enough fuel to build more rpm. This would be a fuel related issue.

I have also seen examples where the throttle pedal can not open the throttle to fully open (or even opens the throttle past fully open and begins to close it again by going past center). This could be caused by incorrect throttle cable adjustment, or something interfering with the pedal being pressed far enough to open the throttle to the wide open position. I've also seen the carb linkage bind and not allow the throttle to open fully. This would be a mechanical issue.

The problem does not have to be cam timing. Gene