Recently bought an 03 rev 3 and have replaced main bearings, piston, plug, oil. Carb is totally clean. Bike starts first kick and runs like a watch. However, compared to my old gasgas and my son's sherco, this thing feels seriously down on power. It's as though the flywheel weight is fitted (it's not just checked) it's slow to rev compared to what I'm used to. Have fitted a fast action throttle which has helped a little. I also took the back exhaust box off and ran it without the air filter but no change. Is this how they are? Any suggestions would be much appreciated.