I got another project machine. It's a 1999 Prairie 300 4x4. I'll start by saying I KNOW I have to tear into it and will but I wanted to get some initial thoughts. The big will start and make a nasty metallic sound and then stall (lots of smoke too). One time it stalled and the motor seem to seize. I was able to get the motor to turn again and then it loosened up. One time it even started and there was NO abnormal noise. My gut tells me (besides needing rings) is that either there is something like a broken piston ring floating in there OR/AND the cam chain tensioner is either not working or broken in the motor. I'm leaning towards the cam chain tensioner because the rattle sounds like the cam chain rattling inside and perhaps a piece of the tensioner is broken off and sometimes jamming the motor. If it was a piston ring I would think that wouldn't jam the motor but if it got stuck between the top of the piston and the intake or exhaust port then maybe. Again, I know I won't know more until I tear it open but was opening for some initial guesses. Thanks!

 

No point speculating, just take the head and barrel off, and inspect everything.