I recently purchased a 90 waverunner 650 lx and my son bought a 93 tigershark the other day. We went out today and my yamaha wouldnt even stay close to him. Heres what I know my compression is pretty consistant around 140 per cylinder,I did adjust the carb cause the plugs were running black and now they are even tanish/brown. It seems to plane out well just not great power compared to the tigershark. One thing I was thinking it might be is when I bought it the guy told me he replaced the water box with a piece of pvc pipe. Could that be it would that throw the power down? What purpose does the water box do?