zack98banshee

I have a 98 banshee that I just recently bought, I bought it not running and put a new top end on it with stock bore and wisco pistons. I rebuilt both carbs, cleaned the fuel system and put new plugs and even coil. It has 150 psi compression on both cylinders it will idle all day long and starts up on first or second kick. As soon as you start riding and getting into high rpm's the left cylinder backfires and stops firing (only running on right cyl) both carbs are perfectly clean and synchronized. Reeds look good on both sides as well. What could it be?

On my stock 98 banshee the left side carb does not have the plastic splash shield that goes over the main and needle jets, but the right side does, should they both? Or just the right. If so what could that cause?? Thanks

just put a fresh stock bore top end on my 98 banshee with wiscos and rebuilt both carbs, stock everything. runs great when first started up then left cylinder putters out, overflow from carb starts leaking until you tap the side of the bowl then it stops and runs great for a little bit, I figured the float was sticking but I took it apart numerous times and it isn't, its all perfectly clean and new internally. sometimes it will die out with no gas coming from overflow, then tap the carb and its fine again. help