Effects if a lighter crank?

We lighten the cranks and flywheels on "real" engines so they rev faster.
You won't gain any rpm it just gets there quicker. The reduced weight will also make it harder for the engine to idle.
 
@ TOTAL_CARNAGE,

Have to confirm what you said:
The reduced weight will also make it harder for the engine to idle.

because after installing my centrifugal clutch, the engine idled quite a bit better, even when idle speed was reduced.
 
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