In my rc experience the flywheel weight can be an advantage or a handicap, the most obvious thing is that your engine will stall more easily if your clutch isn't in proper working order and your tune is not spot on, in my experience stalling once during a main will largely undermine the fractions you may gain with a lighter flywheel, not to mention that a heavier flywheel gets better fuel mileage and produces a smoother more tractable power wich is much appreciated when traction is low.