That is good to know, I have a 150 single seater I was thinking of replacing with a 400EX with reverse. My 150 when stock I used the 40T sprocket but after my rebuild which brought me to a 200cc I went back to the stock 32 T sprocket. I still have plenty of low end but increased my top end by 6 mph. I would check hoe it performs with the 39T first.
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