There could be a multitude of things from the setup as a whole that will make the bike flat. What clip position is the needle in? Timing set at? Reed Petals? Compression? Porting?
Is the bike hesitant, or is it gurgling?
Pro circuits are a low-mid pipe. They only rev to 8,500-8,800 rpm on a stock motor with twin carbs. So your now probably making power to about 8,000-8,300 with that single carb on there. You cant drag race a trail bike, so its gonna need to be setup one way or another. The 2 into 1 intake will accelerate faster off the bottom than the twin carbs. However, it will sacrifice top end. Stay away from the 2 into 1 pipe. They pull really horrible powercurve numbers on the dyno, and are a pain in the ass to ride with. Pro circuits so far have been the best low-mid pipes we have tested and found to work.