So i am building a atc500R with a 1986 cr500 motor and would like to know what size carb would work good on this engine.. Currently it is running a stock PJ series carb.. I havent been inside the motor so i don't know the extent of the internal work, however what i do know is that it has been port and polished, the head has been shaved i assume because the guy i bought it from say's it runs on half 91 octaine and half 110, he said it has high compression although i can not confirm because i don't have a compression tester. i will be running a CPI inframe drag pipe and no air box of coarse.. i am building this bike for all around dune riding and not just a dragger.. so to the question, what carb would really open this motor up for midrange and top end?? I have a stock cr500 pj carb on my atc250r also and it runs amazing so im thinking that this cr500 should run better, Less restricted with a bigger carb?? any help would be awesome and thanks in advance, if you need more info let me know..