As mentioned on other snowmobile boards you need better compression.
Test your coil. See if you’re getting strong spark coming from both leads. Mine pooped out on the trail it was bogging down and didn’t want to go over 25mph until it just diedreplaced the top end and have good compression in both cylinders, but still can't get it to start. Even putting gas right into the cylinders it won't stay running. it pops off for just a second but dies right away.