Wavering, little surges like it wants to pull but can't? Is making revs but not power? Marcus has got it right if that's the case. I would buy the next two jets higher than what's in it, go up one step and try it, and if it gets better but not gooood, go the next higher.
THEN put a new plug in it, try it and when you are in top gear in 2nd or 3rd, clutch it and hit the kill switch at the same time. When stopped, pull the plug and look at it. The porcelain should be cardboard brown, no lighter.
you may need to make a small adjustment to the needle, but get the main big enough to start with.