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big bore kit

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how big of a bore kit can you use in a yz250f in ama. probably be in c class.

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I dont think it matters if its A, B or C class, its if its 250 C or 125 C and in that case you can use any size you want for 250 C.

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You can go as big as you want for the vet/age classes (+30, +40, etc), but I'm not sure how big you can go in the displacement classes (125C in your case). Many people say you can go 2mm over (=262cc 79mm) for the 125cc classes, but I don't think that is true. Someone will inevitably quote the AMA rulebook saying "overbores are legal up to .080"", but I think that only applies to certain conditions and does not apply to 250F's in the 125 class. The AMA rulebook is about to change since 2-strokes can now run big bores up to 144 or 154cc's (can't remember which) except for in pro classes and at Lorettas, but this big bore rule is to make 125's competitive with 250F's, and the rule does not apply to 250F's.

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