I recently purchased a 17ft boat with a 115 Mariner IL6. I took it to a local shop for a tune up because it would stall often around the dock going from forward to reverse and vise-versa. The motor ran great other wise. They told me #3 cylinder was dead and I needed a new stator and switch box (how did it run so good then?). I got it back and the first thing I noticed was my plastic 6 gal tank was collapsed and the vent was closed. I had to use an electric air pump to pop it out. Took it to the river and ran good at idle but fell on its face trying to go up on a plane. It would miss at 3/4 throttle or more and would not go above 4000 rpm. I took it back and complained. They checked the compression and all read 120 psi except #2, which was 115. So they ran it and then #2 came it at 80 psi (shouldn't it go up after running?). They then inspected the piston from the plug hole and said it is pitted and after 1/2 hour aluminum particals from the piston short out the plug. They also had to replace the gasket under the water jacket because when they got it back from me they said it was leaking. I'm just trying to make sense of this. I feel like I paid big bucks to have my motor wrecked! My question is... could doing a tune-up while the vent cap is closed have caused this? What else could all of the sudden make a piston pit and start fouling out a plug? They tell me it just a coincidence it happened when it did.
