Hi all,

I picked up a slightly used KFX90 ATV, starts great, idles good, runs great until about 75-100% throttle then it starts to backfire, at 100% the end of the pipe almost looks like a blow torch. I put it up on a stand and ran it pretty hard for a few minutes and THE PIPE GOT GLOWING RED!! The only mod I was told by previous owner was adding a Pro Circuit T4 racing pipe but I'm beginning to wonder. It may have sat a bit the last year or so. I think they said it has about 80 hours on it.

Any ideas?

Cheers,
Jim

 

try pulling the muffler off and see if its plugged up. and go from there. does it have a spark screen. it could also be the cause. if plugged. heat is building up in the muffler if it glows red.......

 

Check the spark plug color. If plug is whitish color on the electrode and not a tan to medium brown color, machine is running too lean and needs to have at least the main jet bumped up. Could explain why it's cutting out at high rpm,could be starving for fuel and also pipe glowing red.Plus a partially stopped up jet can do the same thing.I'd check into the carb.

 

Welcome to the forums.
I agree with OPT. Get into that carb and make sure all is well.

 

Hey Guys.... Thanks for the quick replies.

I added some Sea Foam to the tank last night and drain the bowl to make sure it got into the carb, then ran it for a couple minutes. Will start today, don't really expect much of a change.

Will pull plug today and remove end cap on pipe. Then clean carb if needed. The air filter was pretty dirty, so the carb may be too.

What's the best way to access the carb. Should I remove the black plastic side panels that have snap buttons? Is there a tool for these? Pliers? Or just take off the entire shell?

Cheers,
Jim

 

Take a pair of needle nose pliers or something and push in on the center of the plastic rivet. Once they are pushed in they pull out easy. Hope this helps.

 

OK, thanks.....off to the garage.

Cheers,
Jim