My near-perfect running '99 335 Sportsman will start and idle just fine but, once I start to drive, it will not run fast. As the revs climb, it suddenly starts to miss, buck and spit and will not go any higher.

The choke position does not affect it. The reverse rev limiter has no affect either.

I've checked the fuel, fuel lines, filter, fuel pump, air filter and changed the plug.

Can I please get a list of other stuff to check before I start changing electrical parts.  

This sounds very similar to the problem I'm having with a Sportsman 400 I picked up.  here's what I wrote:
Bought used 2004 Sportman 400.  Owner claimed ran great before it sat for long time.  Drained fuel and replaced with new plus fuel treatment.  Didn't help after running about 15 miles of fuel through it.
Starts and idles fine.  Runs mediocre when cold at low speed, not at higher speed and rpm (blubbers and craps out).  After 5 minutes of running barely OK, it gets warm and barely runs.  If put choke on, it quits. It runs much better when airbox cover off… but still not great.

Cleaned air filter, replaced cracked carb rubber boot going to airbox and airbox rubber seal.  Thoroughly cleaned carb and all jets.  Seemed clean to start and all jets and passages seemed clear.  Put back together and leaked much gas into motor, leaked out exhaust pipe.  Perhaps float stuck so I removed carb again and re-assembled.  Put in new plug after drying out for the night and still runs poorly.  Removed fuel pump and diaphram and check valves all seemed OK.  

Do these symptoms match yours?  My next move is to get a fuel pump and carb kit and rebuild them both.  We also need to change oil because I think there's lots of gas in the crank case oil.  

You've got my bike!!!!

Yep! That's pretty much what I have too.
I did change the plug. The old one was very black but dry so the mix was way too rich. That explains why choking doesn't help.
I too thought the fuel pump was bad so I took it out, checked it completely including a vacuum test of the diaphragm. It is fine. I changed all the lines and filter while at it. However, in retrospect, if the mix is too rich it's not likely a fuel pump problem.

Since the symptoms are so varied, I've not yet decided if it's fuel or electrical but I'd rather check the fuel system first before tackling electrics so my next job is a carb overhaul. Before that though, since the plug showed so rich, I'm going to check the float level. I usually do that with a clear plastic tube from the outside which I think is more accurate. If that's OK, carb time.
I will also check the timing and do a compression test since they're both easy and quick.
I don't yet completely grasp the reverse limiter system. The symptoms seem to be similar to the way it runs when you try to reverse quickly without pressing the limiter cut-off switch (bucking, missing, etc) so I though maybe there was some connection or relationship to that.
I think it's just a matter of elimination but I want to do all the easy ones first hence the reason for the original post.
Thanks for your reply. Let me know what you think and how you make out.  

I have the same problem also on my 2000 Magnum 325!!! Starts and idles fine!! But it will not rev up. From 1/2 throttle on it bogs down and will not gain any more speed. If I remove the airbox lid it gets better but it is still not 100%.
 I have cleaned the carb 3 times and do not believe I have missed anything. I can't explain why it does this???
 It has turned into a real headache. Someone has the answer, What is it!!  

I am having the same problem with my 2002 magnum 500, anyone come up with a fix yet
thanks
 

Same problem.  I rebuilt carburetor and same thing happened again.  Thought I'd buy a new carburetor but was told something else was wrong but looks like after reading the posts everyone has gone through everything I was told to do.  Has anyone found a resolution yet?  

Same problem here with arctic cat . If any one figures it out let me know.  

I got this off another forum. They said check the secondary clutch buttons, what you all think about that.  

so i had the same thing a month ago... i tok it in and asked them to go through it. after two days i was charged 196$ and was told it was a jet needle in the carb. i dont believe them but try it out.


'08 sportsman 400  

I just started having the same problem.  If anything it looked like the diaphragm in my carb looked stretched.  After calling the dealer they said they had only ever order one.  Making me think that is not my problem.

Planning on giving the bike a good once over again as new diaphragm is $100.  

i have the exact problem with my 96 magnum 425. runs a lot better with out the air box but not perfect. i puulled the fly wheel and found a few loose magnets, actually 4 of the six, the only problem now is finding one that doesn't cost an arm and a leg.. new onw from polaris is $247, tried to buy one on ebay but there is only a few of the one i need and they keep selling for $170 and more for a used one. im still not sure if this is the problem cause i had to heat it up and tap on the puller to get the darn thing off, i swear they weld the things on. hopefully i can find one and find out if this fixes it..... it seems like it could be the problem if there isn't a hot enough spark to burn all the fuel at open throtle, it just seems like i loose spark or theres too much fuel but it ran perfect at idle all the way to about half throttle or so......good luck to alll and if anyone figures it out make sure to let everyone know what it was......  

Hello, I had the same problem with a 325 magnum. I fixed it and it runs good now. The problem with my carb was that the plastic carb body that holds the emultion tube and main jet had shrunk. When I tightened the main jet it bottomed out in the emultion tube and you could see the emultion tube rotate slightly. This gave me the idea that it was not drawing down tight on the plastic carb body. This allowed extra fuel to be drawn in under the washer that sits on top of the main jet. I believe this is what caused the engine to bog down on top end.  To fix this I trimmed about 1/32" inch off of the legnth of the emultion tube. This makes up for the shrinkage of the carb body. I have a small metal lathe so this made the task very easy. Runs GREAT now!! No Bogging!!  

Same problem with a 96 Sportsman 500 just replaced the CDI box