due to the configuration of the engine it is very susceptable to crankshaft resonation which is real bad.
Inline and opposed engines are naturally balanced since the recriprocating action is all on the same plane, while a V formation there is recriprocating action on two different planes.
You don't notice any vibration, but its there. If you don't notice anything now, just wait.
If you want faster reving go for a lighter flywheel. It does not affect the harmonics of the engine and it has a larger diameter than the pulley so even a small reduction in flywheel mass will make for a large reduction in inertia. Inertia is a product of mass and velocity, since the flywheel has a larger diameter, it will have more inertia.
I'd love to stay and chat about inertia properties of rotating masses like, circumfrence x RPM equals tangental velocity, and gyroscopic procession, but I have to go now.
