Hi Mate
The flywheel weight reason is true on a weak engine.
BUT
If you up the hp enough the last you want is a weight dragging it down.
Carby
cam
ports
valve springs
mill out the piston, ceramic coat the top so you can run it lean,
Teflon buttons on piston skirt to reduce drag,
exhaust port it
exhaust pipe it
ignition
or simply
Put me on it, LOL.
Matt