I purchased a 2006 Yamaha waverunner vx110 last summer. When we first got it 35mph was as fast as it would top out at. Well, after researching, I changed the plugs and low and behold 54-55 rest of the summer. The last time my son took it out last year he said it was acting strange again and not running full speed. I brought it home a couple weeks ago and changed the plugs again. The old ones barely had any electrode left. and were toast. Well, fast forward to last weekend and its still only running in the mid 30's. He said the motor is running 8000rpm and seemingly doing what its supposed to do. I bring it home again, crawl under it to check and see if anything is lodged in the prop or drive area. Low and behold, the grate underneath it is completely gone!! Im assuming that would help to reduce the propulsion? Any thoughts? Or would it make a difference and Im still chasing the problem? Thanks in advance!!