Hey Guys, I am brand new to this forum and have recently purchased a Polaris 425 2X4 just to ride my grandson on and take for joy rides. ( I don't hunt and just ride for fun). I am mechanically inclined and had to do a little work to get it "trail" worthy. I have a little problem. After the atv reaches operating temp it has a "stumble" just off idle. When it is cold it does not have this. I believe it is running too rich because the spark plug is black and I get a little black smoke. From what I have read about the Polaris 425 there is a needle valve that wears down and causes the richness in the mixture. I have tried to adjust the screw and it helped very little. (out 2 turns now) I know most of you Polaris owners have probably run into this before. I owned a Honda years ago and did not have this problem. Is the needle valve the only think I need to change or are there other parts I need to purchase to get the right mixture. Thanks for the help!!!

 

Im not a polaris guy but i would say you are correct in your assumtion, your carb is too rich. If it runs better cold and worrsens as it warms up then the mixture is too rich, i would say the pilot maybe a little too big/screwed out. What screw did you turn when adjusting it first? was it a screw on the outside, if so that might have been either the idle adjust or a fuel mixture screw, i believe what you are talking about is the fuel mixture screw. What i would do is open up the carb and see how big the pilot jet is, and if it is screwed in our out. Screwing it in slightly might help.

 

I just got through a similar issue with mine. You probably need to replace the jet needle and the needle jet. Don't get the needle jet confused with the main jet. The needle jet is what the main jet screws to. Here are the part numbers: needle jet 3130510, jet needle 3130528. You may want to replace the needle and seat while you're in there, 3130531. Mine was so bad that you could see the wear on the needle jet, it looked like someone drilled it out larger.

 

Thanks guys, I will try these repairs and let you know the outcome. I will have to order the parts so they will be here before I open up the carb. I don't think the parts are too expensive.