looks like its been doing this for a little while
Center cylinder I think looks perfect, it has all the right stuff showing on it,mag side a tad only rich, but this can come from extended idling/low speed lugging. The pto looks like its been melting for a while now, not just all at once.
What I am about to say dont take the wrong way!!!, but the tempa-blow you have on caused this in my opinion from what I can see in the pics. Its been leaning the sled out after you have hot air under the hood. Like this scenario: You and your buddy's have been running fairly hard thru the trails, and suddenly you all come to a intersection, and naturally you stop to make sure everyone all catches up, you look at a map for a minute, Everyone takes off, including you, goose the sled up to 50-70mph, wham, the tempa blow leans out the mixture and until the airbox temp drops again, it continues to run lean.
This is a classis case, I have seen this many times before, (fixed many from this same problem)thats why there is carbon on top of the melted section on the pto piston. When you have a sudden problem it doesnt put dried carbon on the melted area and cover up whats been taking place over a span of time. just looking at the pics, looks like the carbon is on top of a drooping center crown to exh port edge.
With the mods you have the jetting would be very acceptable and should provide more then crisp performance.
