Where is your timing knob set?
What jetting?
What notch is the clip in the needle?
Are the cylinders still nicasil no sleeves?
I checked my timing running and my mark runs 1 degree retarded, so I run the knob at 0 which is one click safe. I could click to +1 and still be fine with no less than 93 octane. You want to run at 0 degrees advance at NLT 91 octane. Your timing may be off (advanced) a degree or two and not know it. This would burn the fuel faster and not show any or minimal piston wash. I ported and flowed cylinder heads and anything else I could fit on the flowbench for 7 years in a race shop. I have over 8000 hours of experience on the flow bench. A slight port cleanup could affect your jetting. You may have to jet up and adjust your needle accordingly. I found that mine is pretty sensitive and easy to find the jetting "sweet spot". I am running 320s with the clip in the center notch. My pistons are dark with a slight wet on the edges. I run the BR9EYA's. They run the nice "lunchsack brown" I have no bog and it pulls from when I can the throttle till it hits top end on straightaways. I have never had a bog-very smooth. Turning the knob up will not benefit in the trails or on the lake. It is for sno crossing with higher octane/race gas in short bursts. When you find your timing, do not move the knob more than +1 degree( 1 degree advanced after you see where your timing is). As the temp cools down to 10 or less, you can back it down a couple clicks and save changing jets, but power will be down SLIGHTLY, but noticable(plugs will also be darker). I leave mine set at 0 degrees( because my mark show advanced 1 degree), 320 jets for hard running in trails-I mean hard running, but flippin the throttle a lot to keep fuel to it and the lube pump pumping. You have oil injection, right? I used Klotz oil, have for 15 years and never had a problem with it. I have started this year using Amsoil Dominator oil because I ride my sleds hard most of the time. I have not seen any problems yet and don't expect to. I have never run Cat injection oil or APV oil in my sleds. You are probably running close to the mark on jetting and okay, but going a little richer doesn't hurt to get some wash on the piston. I would like you to be able to see a little more on the piston. I hope this helps