Hey guys need help. First boat ever. 1988 BAJA 220 sport has a 1989 GT300. I bought it 5 months ago and just took it out for the first time. It seems to start ok and idle fine )as long as I don't rev it up in nuetral).I can take off WOT for about 15 feet then there is a shaking of the motor and a sound as if it were a new car being floored when it is in park. woom woom woom woom. Even if I take off slow and gradually give it more I can only get up to about 15 mph if I go 10 mph it runs perfect and is very sound. Just can't go any faster than than 15. RPM guage doesn't work but I would guess it maxes out at about 2000-2200 RPM's before this problem occurs, and I know they are gas hogs but I rode around for about an hour and 15 min. and used 13.4 gallons of gas. I have ZERO knowledge of any watercrafts. It does have a 4 fin prop, a power lift that doesn't work so the motor is set all the way down. Pulled plugs looked ok. There was a more oil on the 2 right side lower plugs. Any pointers??? Thanks