While riding over in northern WI last weekend, I encountered a major problem . 15 miles into our ride, the motor slowed for about 2 seconds and quit. I pulled the plug, and it was light brown(normal). We pulled it back to the trailer, and pulled the pipe. Piston is pretty much scored. When it happened, I was running about 3/4 throttle to wide open, varying speed.

History Aaen top-end pipe & silencer, re-jetted, and AAaen clutch springs) has been burning more oil than usual(compared to my Explorer)ever since it was new in April. Pipe was installed prior to the ride, and re-jetted. It ran crisp up until it died, maybe a little rich on the bottom when cold. plug appeared OK, but yet the exhaust side of the piston is scored.
Theory #1: carb was running lean in mid-range, but OK on bottom & top-end.(Polaris dealer theory)
Theory #2: pipe was not warmed up sufficiently between head and cone of the pipe, (45 degrees air temp.) thus causing unburned fuel mixture to burn close to the head. Pipe should have been wrapped to keep warmth in, because the cool air hits that area directly.
Please enlighten me, which is more accurate?

Pete Niska
99 Scram 400

 

I had Sport 400 with AAEN top end and from all i knew and what i learned Theory #1 sounds more probable to me.