Hi all! I have a 2000 XR175 Sportjet, I was running up the Sky (been running for about half and hour) when the motor started dropping rpm's quickly and knocking, I shut it off. I jumped on the trolling motor and got to a safe spot. Started it up and it was knocking but couldn't tell what it was, shut it off and cleared the pump via the stompgrate. Started it up again and it was fine. Jumped back up on plane, about 15 seconds later, lost power again and this time it froze.

The mechanic said I had lost a piston due to detonation. The rest of the motor is in great shape, pistons and all. The shoulder of the piston about a quarter (a little less than a quarter) of the way around was gone about a quarter of an inch down. Spit the rings, etc.

I am curious if anyone has had similar problems or any input on this event. The boat is up and running again now, new head, bored one cylinder and new piston. They said it was due to bad gas.

The boat was run only 5 times or so a year for the last 2 years and I always kept the tank full (to keep condensation down). Would add gas when it got down to half a tank. Has a 50 gallon tank. Anyone else experience this or is it possibly something else? Thanks for the help.

Doubletake