05,660,4×4,grizzly starts fine , idles fine , but you get it warmed up good and it will backfire ,1time or it may backfire 5,6,7,8 times. then it goes for ? miles and do it again.dont matter if your getting on it or letting off it, random. havent tore into it yet bc i dont know where to start . thinkin valves or springs, gasket maybe,carb? thanks for your time.