I have a 2006 sportsman 500 EFI. It will idle fine for a long period of time. However, after you run it for 20 minutes or so, it will start to sputter and occasionally backfire. It really started to misfire when needing extra horsepower(hills, mud, etc). Also, if you let it cool down, it will run OK for 15-20 minutes again. Any ideas?

 

First thing I'd do is have the fuel pressure checked. Must hold 39psi without any drop. If fuel pressure is ok,then it could end up being the old problem of shorts in the map sensor wiring,especially since it back fires. Codes may not be thrown. Problem can also be intermittent. Read this about efi problems,related to the 500 also.http://forums.atvconnection.com/pola...ap-wiring.html Plus mentions this site for stronger harness repair kits.http://www.otbpowersports.com/otb-powersports.htm