The 58.5 cylinder will not alone require a rejet unless one has not been done yet since these machines leave the factory lead running for EPA reasons. You will definitely need to rejet if switching to an open air filter system that is getting rid of the restrictive air box, adding a head upgrade or camshaft.Unless you are making some radicle changes to the motor such as stroke with 62 or 63 mm bore and cam with lots of overlap your carb is sufficient. A larger carb will actually hurt performance. Cams are ground for different purposes More lift with little overlap is best for hills, the more overlap or duration will increase top end, so it will depend on what you will want. With the available cams for the GY6 my preference would be the A12 cam. If you want seat of the pants power enhancing your bigger bore a quality performance head ported and polished correctly along with the A12 cam will produce some surprising results. Even better a Quality 4 valve head which comes with a sport cam will give the best results. Regardless on what you decide the key are quality parts. With quality parts properly specked you will have great power gains but most important you will avoid the many failures cheap parts will bring.
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