It was doing it when i got it and since then i have rebuilt it with different cylinders,new reeds,shaved head,reed spacers,boost bottle and cleaned the carbs and sync em repact the exhaust cleaned inspected the intake boots all new gaskets. I went .20 over vitos carbon fiber reeds fmf gold series exhaust with 200 or 210 mains but the noise happens after you pretty much get it warm and its like a woof or a puff its hard to explain and even harder to figure out but it does it kinda mid rpm and low rpm only on acceleration but any help would be cool