Seadoo 657x hole in piston

[Mraw]

Hey all, got a 94xp for very cheap. Comp is 150 exact in each, before i spend money on I took a look at the pistons, one is fine but the other has a hole in the top. Curious on what causes this, ski did have grey fuel lines and carbs were gunked up. Pistons are marked 77.95, is this stock? Ski has a wiesco sticker on it, will they be marked if they are wiescos?

 

[AKnarrowback]

Detonation.

Seen it a million times on sleds. What is really cool is when it burns a hole through, like it got shot with a .30 cal.

Typical causes are a lean condition or bad fuel.

For you I would suggest complete carb rebuilds with genuine Mikuni parts. Confirm the fuel system is air tight. Make sure you have good gas. Double check the timing. That is for starters. You also need to confirm all other aspects of the machine (intake, exhaust) are sound.

The Piston needs to be replaced, it's damaged and I have seen pitted domes cause fractures later that take out the case, crank and cylinder.

This is my view. Lots of good guys with lots of experience to add in here.

 

[Ckrawiec]

IDK......but if a piston has a hole in it...how did he get 150 compression in that cylinder (according to the original post)????
Certainly looks like piston degradation, but not burned through (YET!) to my untrained eye