Service manual for a 2006 500 Polaris Sportsman HO

I have a 2006 Sportstman 500HO ATV, EFI. Sometimes it will run 100% correct, other times it will start, idle fine but then when giving it throttle will will start to surge almost like it's hitting a rev limited. Sometimes it will backfire and stall. I already replaced fuel filter, flushed the fuel lines and gave it fresh gas and installed a new spark plug, but no good. I also checked the throttle switch and it's not making contact to stall it. I download the service manaul and tested each sensor and they tested fine which is probablt why I get no check engine light.
This ATV is mainly used to plow snow in my driveway, no salt. It's used around my property but very lightly. It's still as clean as it was when I bought it and it doesn't have but about 40 hours on it.
Polaris 500 HO EFI 4x4 ATV: Vin# 4XAMH50A56B707664 purchased 6-8-2006

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Hi try cleaning the carb or check your air filter box might be filled with oil so all you have to do is clean the air filter out with water let it dry and soak all the oil up with a rag or sponge. Best of luck!

Hi look for a pinched spark plug wire under the fuel tank,seen it many times,you can just un screw it from the coil & pull it out.mike