Burn down, question on these pictures, please comment

Catsledman good read

But I have a few questions. Are you saying to run Skidoo XP needles in 2nd from top position? I was thinking that on another thread you said to run old ZR 3 cyl. needles? What yr. of XP needles are you using? Also do you richen up the fuel screws down low and say maybe 2000 ft. up at the bowls you turn them back in? I like you have ran from the truck burbling at idle and just playing with the throttle at about 15 to 20 mph this is about 2500' Then at higher 3500' and above I give her hell! Also I noticed as you increased the midrange richness you said to increase the mains as well, but as a last change. Do you feel that with the stock 360's it was a little lean on there jetting chart? I for one when riding with other sleds(Polaris 700 edge models) always have more fuel left in the tank. Is this due to the lean jetting or just the larger CC's not having to work as hard?

thanks Mike

Just put my 04 back together, had the same looking piston but not as bad. I traced it back to some e fuel that a station had put in but did not have an e-fuel sticker on the pump. WORD OF CAUTION THERE ARE A LOT OF STATIONS GOING FROM E-10 TO E-15 THANKS TO OUR GOVERNMENT. With this fuel you can't let it sit and need some water drier so the fuel won't adhere to the water which in short leads to low octane,which in short leads to burn downs. Just something I found on my sled. My 2 cents.

Just a little something to think about. The 900 has a wicked lean spot in the mid. Riding down a road for 2-3 at steady throttle will melt the pistons. Even stock you need to keep the throttle moving !! Also, I ALWAYS stagger jetted my 900s. Run 1 or even 2 sizes bigger in the mag side. At 7500 - 10000 I ran 330 pto and 340 mag. I don't think your jetted to lean, I think you just burned her down riding down the road. From now on keep the thumb moving, no steady throttle unless it is WOT.

I don't know if this will help but I had a polaris 800 that had a spum ring or else installed wrong. And one side of the piston had no scoreing but the other looked like there wasn't even a ring on the piston, It ended up breaking the skirt of the piston off and sent that into the crank. Don't know if this is the case but, something to think about.

looks like a lean burndown. You may want to check your mag side crank seal. If it has a small pin hole or is leaking it will cause a lean condition. This is one of those phantom problems that will drive you crazy trying to find out what is different from the last x years of riding. Good luck.

As CATSLEDMAN said some engines like to be a little rich.
Your PTO side is TO lean and as Rixster said staggered jetting !
Have any of you guys with carbs try just grinding a small flat spot on the needle around the throttle position that is to lean.

That Cat motor is very forgiving on rich jetting... you can run it pretty rich without affecting performance. So bump up the jets a couple of sizes. Classic lean burn down with the exhaust side chewed away like that... only thing more classic is a hole drilled in the middle of the piston. Once the alum starts to melt away then it coats the cylinders and makes them look nasty like you have.

sled_guy