Okay, this is my buddy's ski but my wife was riding it at the time so I feel I gotta do what I can to make it right. I've wrenched on my Polaris 780 so I feel I can tackle whatever is wrong given the correct instructions.

The wife took it for a ride and I noticed when she first tried to start the ski that it didn't sound right. It sort of fired but didn't just pop and go like it usually does. She rode for about 10 minutes (nothing to radicle) and then picked up my son from the boat and took him for a very slow speed ride. We saw her just floating a few minutes later and she said it didn't seem to be running right. My buddy said it had been dying on him a lot that day and thought maybe the plugs were fouled (he hasn't put new plugs in it in 2 years of ownership). So he got it started but it was definitely doggy and he limped it over to the dock.

When he got home he pulled the plugs and found the front cylinder to be tan colored. Great, from that description it sounds like that one was burning fine. Unfortunately the rear plug was black and wet. He did a "thumb compression" test and found nothing on the rear cylinder, the front easily blew his thumb off the hole. We'll get a real reading with a gauge before we dive into the motor.

This is a bone stock ski. I haven't pulled the head yet so I don't know what we're looking at. I'm not sure if it's a holed piston, lost the rings, or what. There was no knocking so I'm pretty certain the bottom end will be okay.

I'll post more info with pics when I get it torn down, but in the mean time I would greatly appreciate any advice if there any "typical flaws" with this ski that I should look for when repairing this cylinder? Like I said, I can wrench on things just fine but I've never worked on a power valve engine so I just want to make sure I have my bases covered. I want to be sure we find the cause of the problem because I know if we just throw another cylinder in there this will happen again.