My 2000 kx250 ground up rebuild came with a sleeved cylinder on the stock 66.4 bore. I've seen pistons up to 68.4 and every size between and was wondering which oversize is advisable? The stock sleeve is fine but I'm starting out with a fresh bore. I'd prefer to not have to shave the main valve so it might even take less than a mm over bore if it keeps me from altering the main sliding valve.
