I’ve got a 2003 Grizzly 660. Sometimes it will act like it is going to cut out and die, but most of the time it will keep going. On a few occasions, it has died, but not very frequently does it do that. What could be causing this?

I am wondering if it has something to do with the HMF slip on exhaust and K&N filter that came on the bike when I bought it?

The reason I say that, is it almost sounds like an air issue to me, but I am no mechanic.

Any suggestions on where to look first?

I thought about putting some premium fuel in it just to see if that would help.