My Sportsman runs great under acceleration, but pops and backfires when decelerating. I changed the spark plug (twice)...it makes no difference. Could this be a fuel filter problem. It starts good and idles good.

 

Welcome to the forum! Could be a map sensor wiring harness problem causing the backfiring. You can check the "sticky" in the expert section on efi harness and connector problems,plus you can check the wiring coming from the sensors on the throttle body for any bare wires or if any wire feels soft (could be internal breakage) Plus check the crank sensor wire harness where it rides close to the starter for any bare spots. If you haven't changed the fuel filter might be a good time to do it. Plus excess throttle slack could cause this. Thumb lever should have about 1/8" slack only. OPT

 

I had a backfire issue on my 06 X2 and it ended up needing a new battery. I got the new battery and the issue went completely away and a few rides later started again. It would stall, backfire, and hesitate at times. I checked the connections on the battery and they were loose. I ended up using loctite on the threads with star washers to act like lock washers. Been running well since then.

 

I haven't found any loose wires. I did take it for another ride and determined that it runs great when the engine is fairly cool, but when it warms up enough to kick on the fan, that's when the engine will pop & backfire. It feels like a timing issue.

 

If you haven't ever changed the fuel filter,might be a good time to do so.Timing is regulated by the ecm module.If cam timing was off it wouldn't start and idle well. Make sure that all connections are tight and you are charging around 14 volts back to the battery(if you suspect the battery have it load tested). Also the throttle slack(1/8" max) if you haven't checked it already. Could be a voltage drop if it only does it when the fan kicks on (weak battery,loose battery connections),but on an efi system you can't rule out internal sensor wire breakage(check for any soft wires), connector problems, or even the smallest break in a sensor wire from the crank sensor harness all the way up to the tps and map sensor harness.Seems like most of the harness problems I had were intermittent. Would run good for awhile,then erratic backfiring, surging,etc,either coming back down to idle or at idle.Also make sure the foil under the tank is secure to help keep heat away from the tank that could cause pump problems when engine is hot . If you access to a fuel pressure tester,with just the key turned on and pump primed up, should be holding a steady 39 psi hot or cold. This could eliminate any fuel pump pressure regulator problem. OPT

 

GOT IT!!!!! I started to pull out the map & tps sensors to test them, and noticed that the throttle-body wasn't attached securely to the head. Some how, the clamping screw had backed off allowing air to be sucked in. Tightened everything up and it runs great now. Thank you!

 

Glad you found the problem! OPT