My sp 400 2002 1000 miles just started to backfire and won't idle all the time. I ve taken it in for its maint. and don't want to have it hauled in again. I don't have a trailer and have to pay to get it hauled. Would a new plug help? or maybe anthing else i could do myself? Also is it hard to change the oil and filter - do you recoment the kits the dealer sell to do it? thanks i'm new to this - it for my kids but i love it now

 

its most likely thats its the spark plug they make four wheelers backfire and not want to idle and not even go after they get so bad. just go pick on up for like $3.75 or so and put it in and see if it works

 

Try adjusting the throttle cable so you have about 1/8 inch freeplay in the throttle lever. This was the problem in my case but I have a 500.

 

check out your air filter and see how dirty that is, clean it up and put in a new plug and your ready to go.