How to find a smaller flywheel ? Engineers ?

1WildRT said

Not understanding what you are hoping to accomplish..

Gear? So there's a gear to mesh with? Or a sprocket to engage the chain? any access to the end of the crankshaft?

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I will use a Mopar starter to turn a roller that in turn spins the wheel on the bike. Once up to speed I let the clutch out and essentially “Pop Start” the bike .
They are fairly common in motorcycle racing but cost a small fortune. And I have most of the materials to fabricate one .