FS570 11' Backfire and now power

Took the 570 out today. Should not that it is a snow bike and I've taken measures to keep the engine at or above 150F. (primary cause of most snow bike failure is a cold engine)

Anyways rode out to a friends cabin. 10-15 miles. ran fine. tons of power as always. Shut the bike off to go inside and eat. when i came back to ride more. it would hardly start. cracking the throttle at all resulted in a no fire but would still crank. Took a good 2-3 of trying to get it to start to get it actually fire. once lit i had to keep the throttle cracked to keep it running. put it in gear and it was like i was trying to move the space shuttle. I had to rev it and then basically pulse the clutch to get it to move. once moving the thing was back firing the entire way home. could never get above 2nd gear with out it nearly dying again but even that 1st and 2nd had almost useless power.

In my head i've come up with a few things i need to check.

- Leak down check to see if maybe the piston is shot.
- fuel filter, maybe its just not getting enough fuel? seams unlikely but easy to check
- pull the plug as see what it looks like lean/good/rich?
- Check and change the oil.
- Do a valve check.

I should note that i have had a rock arm size up on this bike before. but that resulted in a total no start.



Anything else i should check.

I fell like i can rule out electrical and/or ignition. Im getting spark, Im getting at least some fuel. its revving when not under load.

I shoul be more specific about the starting with the throttle cracked. I more or less had to time the firing of the engine with cracking the throttle to take it off idle and get it running.


I check the filter out there and it was bone dry and clear as a bell. We run snowmobile pod filters with snow screens instead of the big foam one. They just turn into ice blocks with in minutes. Also the snow yesterday was wet and wasn't getting up on the motor. It also wasn't that cold. 25-30F degrees. I rode earlier this winter with -20F.

I semi already checked the pump. When i turn the kill switch off i hear the pump run for about 2 seconds then turn off. And I also disconnected the fuel line and held down the valve and it sprays out with good pressure. No PSI reading as my finger is not calibrated. Lol

Im heading over now todo a leak down check and some simple stuff before I go nuts tearing it down

I just finished my leak down test. 3% blow by... well with-in acceptable ranges.... i feel much better about the cylinder now. next up are clearance checks. TPS check... any others?