A friend of mine has a 2000 1100 stx di. After riding the ski just didn't seem right, it would hesitate and the rpm's would fluctuate at high speed. Also the check engine did come on once.

The engine and pipe felt hot to me, but i'm not familiar with Kawai. I'm guessing about 120 degrees. I ran the engine on land with a flush, this time the pipe stayed very cool, but the block was getting hot.

We pulled the plugs, and all 3 cylinders had a lot of carbon buildup on the plug (new plugs)

Any suggestions?