I've currently got a really old fmf exhaust that's been on there since I bought it in 2000. I rode it for a month or two before I gave it to my brother for his car I wrecked. Just got it back this last Christmas and there are a lot of issues, so I'm trying to add more horsepower out of the engine since I want extended swing arm that weighs more, and today I weigh 205 lbs! 10+ years ago I weighed only 140 lbs! It used to be bored out bigger but my brother took it back to factory cc's. should I go back to bigger bore once it is time to rebuild? Would it make much difference? Right now the motor seems week and I can't just floor it, cause the engine spits and sputters. I've had the carb professionally cleaned, I've changed the jetting down fron a 205, down to 165 I think. I did that cause I thought it was flooding itself out. It is a little bit better now,but still not like it should be. My brother said I should be spinning on the loose gravel through almost all gears but I can't get the engine to rev up very quickly. I have to slowly get into the gas, I can't just floor it.