burnt spot on piston by exhaust port, possible bad RAVE valve?

[2001GTXseadooRFI]

So the cylinder cracked over the winter on my ski. While taking the engine apart I noticed a burn spot about an inch by an inch. On the piston exhaust side. By the exhaust port. The other piston does not have this burn mark. Its a 787 Rotax RFI engine in a 2001 GTX RFI. Engine was rebuilt before I took ownership of the ski last year with only an hour or so on it. I've put about 40-50 hrs on it since the rebuild. ran the ski at 3/4 throttle or less, varied rpm and put an extra cup of oil or so for the first three tanks of fuel. And i only used the seadoo syntheic oil. Annoyingly expensive. The RAVE valves looked ok, weren't excessively dirty or heavy carbon deposits built up on them. Just goopy oily build up. Appear to be factory cylinders with unkown aftermarket oversized pistons. would like to know if a rebuild or replacement of the RAVE valve is necessary before I put this ski back on the water. Any thoughts?

 

[Dr Honda]

A burnt spot by the exhaust is caused by a lean run. The RAVE probably didn't have anything to do with it. Also, your break in has nothing to do with it.

Possible problems:

1) On the RFI engine... the computer shuts down one cyl at idle. If the injector is leaking any fuel... it will be enough to run that jug hot, and start eroding that piston crown.

2) If the injector on the Cyl is going bad or slightly plugged up... it could be running lean up top.

3) If your fuel pressure is a little low... the PTO jug will show a lean condition before the MAG jug will. (which piston is it?)

Before putting it back together... you need to figure out what is happening, and replace that piston. Also... problems 1 and 2 both can be resolved by replacing the injector.

Can you post up a pic of the burnt piston so we can see how bad it is??