My Rancher 420FM just started having problems his year and not sure what the issue is.

The background:
A couple years back I flooded it but got it working fine again.
Rode it last in june 15. A couple minor starts in fall.
A few months back I started to plow the drive and it started fine. Started plowing the driveway and then the motor would cut out. I'd start it wand it would backfire. I thought it was bad gas and te tank was quarter full so I filled it. The problem continued. I always use gas treatment so I don't think it's bad gas.

Today< I pulled it back out and gave it an oil change. The Rancher started up fine so I took it for a quick spin to warm it up. Started fine but when it got warm, it started to stutter. After the oil change, I took it out again and same issue. Stuttering on acceleration. It's almost like a governor is kicking in and won't release until I let off the gas. No backfires.

Any ideas of what's going on?

Thanks.

 

Fit a new spark plug. If that doesn't work, there is a "tea bag" type filter in the fuel pump housing, fit a new one. Also a fine mesh filter in the top of the injector. Remove the injector and clean it by poking gently down the top with a tiny screwdriver and blowing out with compressed air. You need to take out the strange electric motor driven plunger to get at the injector, this is very fragile, so be extremely careful with it.