My buddy's 2004.5 Sportsman 400 backfires and looses power after it warms up. He took it to the dealer and they replaced the coil pack but still experiencing the same problem. Any advice is much appreciated.

 

Check the plug wire, follow it back from the plug to the coil as some were being pinched between the frame causing them to misfire or no fire at all..........

 

EFI or carbureted model?

 

got a 500 ho had the same prob. the speed sensor behind the speedometer was the prob for me..

 

cam!!!! its the cam ill bet money ours did the same thing

 

Take a look at the throttle freeplay.. Adjust accorging to your owners manual.

 

Pinched spark plug wires are the big thing this year for 400 and 500s. I have not heard of a build date range but there have been alot so far and if you run across a Polaris stuck in the woods with no spark check that.
400s are jetted a little rich on the late model 2004s. Replace the main with a 162.5 for best full throttle performance. The jetting issue really shows up on long steep climbs.

 

my 2004.5 400 had the same leed problem, jammed between the tank and frame. Wore through and stopped running. Mine is 9 months old now done 250 hours on clock. Just starting to have carb problems missing a full throttle again. Jetting was changed from new and was fine untill now. The old 335 I had a lot of carb trouble.(did 9000miles) This is the bikes biggest weekness I believe. Other than that an awesome bike. Recommend it to anyone.(till it lets me down). We will see I guess.
Cheers all
Scott

 

hey back40 i have a 2004 sp 400 about 3 week ago i took it out for a ride it ran ok for about 1 mile then when i would give it throttle it would get up to 10 to 13 mph and would mis and about go dead but it would catch and run good until you let off gas and it would backfire and do the same thing start missing at that speed and catch up and go. after fighting that all day i got back to house and started looking for loose wire pintched wire anything out of order. i was looking at carb on the back of carb there is a clear fuel line it is a breather it has a tee two line going to carb and one going to left side to a hole in the frame to vent i was looking at the vent in frame and saw spiders in there hundreds of the things i pulled the line out of frame and the damm dirtdobbers had it stoped up i cleaned the nest out and it has run great every since. it only took them one day to do this.