Alright I've tried alot of things before writing this. I got a 2012 grizzly 300 2x4. Picked it up used a couple years ago. Don't ride it much as I use my bruin more. It never seemed go run quite right, I never seemed to be able to run the quad without the choke on a little for a long time then I could take it off. Cleaned the carb and it didn't help. So now it sat for about a year and it wouldn't start. So I pulled the carb and all jets and cleaned everything out because it was all plugged up. Put back together and it started up but with the choke off any movement of the throttle and the bike stumbles, back fires and dies. I took the air fuel screw cover off and tightened it all the way in and then out 2.5 turns. Same thing. Checked the plug, it's black. So where am I at now to check? I'm at my max for my knowledge of what to check. I'm not finding much online for the 300's. What are you guys thoughts?