I have a 99 sportsman 500 and for the past two years I've had your exact same problem. The local Polaris dealer took my money and could not fix. I had an after market exhaust on the bike that leaked bad between the manifold pipe and the header pipe, I was thinking it was the coil that was not working 100%. So I changed the coil ( Kimpex ) 25$ and put on a stock exhaust at the same time. So I can't tell you what fixed mine but that's what I did. It runs great now. I changed my cam, new ring, cylinder redone, reseated valves, put new gas with seafoam, cleaned the carb, rejeted, and that did not fix the problem. The coil or the exhaust fixed mine. I lean more for the coil.

 

Well, I changed the cam today and I still have the same problem I had before. Before I changed the cam the sputtering got worse now its anything over 1/4 throttle. This is really ****ing me off. Ohh the sparkplug was completly black like its runnig extremly rich. The now plug has no more than 3 miles (if that) on it.

All stock - where did you get a coil for $25 I might try this.

 

I got it on ebay from sledpartsguy it was a buy it now item. I'm in Canada and he was in U.S. it came to 33.00 Canadian with shipping and that was on march 13 of this year. I just cheked he has some now on ebay.

 

Remember to disconnect battery when working with electrical.

 

All stock- I just ordered one today from the same guy on ebay. I really hope that is my problem because I really havent been able to enjoy my quad since i bought it...

 

I know how you feel. The whole time I was working on my bike I was thinking coil but was not willing to pay 180$ for an OEM coil. I had given up on my bike but when I found that aftermarket coil on ebay, I had nothing to loose. I am confident we got it because my problem did not just go away after two LONG years.

 

keep us updated.... I would have no hard feelings toward this bike if all it takes is a coil to fix our problems.... /fingers crossed...

 

Results of the new coil are in and.......

No luck still the same sputtering crap. Its running extremly rich, I can smell unburned fuel out the exhaust and can see some light smoke

 

Have you tried adjusting your valves? I have and I got better results (higher rpms) but still acts the same. The best results I have had are from removing my airbox and sticking my hand behind the carb fluctuating the amount of air it gets and from that I can get my bike to rev up high like nothings wrong with it, but as soon as I put the airbox back on my bike just falls on its face and keeps sputtering. I am at a total loss, I have gone over every inch of this bike and just cant figure it out.
Keep me updated, I will do the same..

 

Sorry to hear it still sputters! The only thing other than the coil that I did was my exhaust leak between the manifold and the header pipe (doughnut). I did top up the battery and charge it. Last fall I did put Sea Foam in my tank But it was still sputtering. I wish I could be more helpful. I'm going to try my old coil to see if it comes back.