too hotI
I recieved two phone calls this week on burned down king cats with carbs.
One old friend has burned won his 900 3 times, dead stock, its been a spare sled for the last 4 or 5 years, xmas vacation his visiting son riding at 25mph at Lolo pass here in mt. Pistons and jugs are just like your pictures. Since he bought this sled in 04 I have never been able to convince this ex dealer to jet his sled properly. Your piston that did not seize is way way lean. Absolutely no wash. the wash you need on this sled with carbs is nothing like what you might see on a late model efi anything so don't go there. For this old twin to run and have lots of power you need big thumb nail size absolutely dead clean to the aluminum bright piston wash. If you have never been there, you will have no idea how strong this old motor can run. Stock jetting they are barely there.........oink oink.
One of my good pals that I have tuned sleds with for 30 some years called about his neighbors newly aquired king kat big bore union bay way wooped sled. Suposed to be a giant killer. Previsou owner mortgaged the farm for this toy............that didn't impress. One ride around the pasture and Tom called because re recognized that the old girl was scarely lean and wanted to know about what we used to do to make these bullet proof. few hours they put in bigger pilot jets, each step it ran better, threw in a set of new rich xp needles, it starting spitting and burbleing and running so hard the 5 acre pasture was no longer a good testing site, went up to 420 main jets which took the mid range burbble out and the next day had the first faint signs of piston wash. Not a stock 900 but typical of where you have to go to make that old twin sing without choke'n.
No nice piston wash, the engine is slowing dying of too much dry sickly heat.
In my experience you don't have a malfunctioning broken part that's causing your problem. You simply have an incorrectly jetted snowmobile. If you own one of the old cat twins withouth piston wash no matter how far or how long or who used to own it, its headed for the aluminum scrap pile.
this stock lean condition is agrivated by the timing curves that change on this sled as about 1/3 throttle. Clutching, gearing, track, rider habits, snow conditions on the wrong day will will end your engines life. What you don't see is the damage being done in engines like this on the day the thing still lived, just becuase you made it back to the truck doesn't mean its running ok.
Your pictures are likely a snapshot of the end result of a sled going down slowly every day its ridden. Not a pleasant thought.
Worse, there's no one easy answer. Jetting can take time, testing, two steps forward and one step back. No fun for lots of folks especially without resources. Thats why EFI.
