Re: 9 tooth drive sprocket (or less?)
I believe this question was asked and answered. It would be much easier to replace the rear sprocket with a larger one than to locate and replace the engine drive sprocket. Hill climbing ability is increased with a larger rear sprocket which are readily available from numerous sources. Standard sprockets supplied with most kits are in the 40 to 44 tooth range and are good general purpose sprockets. Moving up to a 48 to 54 will give you better hill climbing performance but will hurt your top end speed as well as allowing the engine to run at higher RPMs. You might find a smaller sprocket for the engine but it is not a standard size bore and might require some very expensive machine work to get it to fit and then you're restricted by reducing the tooth count(sprocket diameter) by only a couple of teeth which won't help you that much.
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