my sportster runs good but doesn't have much power. It will reach 6500rpms but not get much higher. I have never owned a 4 stroke before and I know quite a bit about the two strokes. This is not a cavitation problem. I am going to replace the plugs tonight but what else could cause an issue like this? I noticed one plug was slightly whiter than the others and the others had some oil on them. Is that normal 4 stroke behavior?