The symptoms:

Between 4,000 and 5,000 RPM (currently) the engine will not hold a constant RPM with the throttle held at the same position. I think the problem was at a little higher RPM when it first showed up, but we did not take notice of the RPM range then. Trying to hold the RPM steady in this range causes the engine to hunt between 4,000 and 5,000 RPM. It seems to me like the engine looses spark for part of a second and regains it at 4,000 RPM. I suppose it could also be loosing fuel for that short time.

Things that seem to have been eliminated by me and the dealer so far:[B]

- It is not a faulty tether switch. It happens with the switch removed.

- It is not anything faulty in the throttle safety switches or the kill switch. It happens with them removed.

- Its not a tank venting issue, as when it was happening one time, I removed the fuel cap and replaced it. As soon as I moved off, it happened.

- It is not in the stator, as suggested by Polaris customer support. A new stator was installed, and the problem happened again.

- The problem does not seem related to engine temperature, as it has happened when the indicated temperature was below 140 degrees F, long after the engine had been indicating in the 170s.

- It does not always take a long operation to exhibit the problem, as I once tested for it at home, after removing the drive belt (so I could see if the belt or clutches were part of the problem and I would not have to run the track), and it happened immediately on starting in 40-degree F ambient conditions. (FYI, I was lucky, as I only ran it at low RPM with the belt off, and the dealer told me that with the belt off, the drive clutch could close up too much and throw its weights. Lesson learned the easy way.)

- Once the problem starts, it seems to persist for that ride. We have put in new plugs while riding, and as soon as you ride off, the problem is back.

The problem first happened after 50 miles of riding, and once it started on that ride, it was persistant till the end of the ride. That persistance to end-of-ride seems to always be true.

This is my wifes 151" RMK, and my otherwise identical 159" RMK does not have this problem. The only other sled difference seems to be that hers uses oil at an average of 42:1 and mine at 58:1. Mine gets ridden a little harder, so I'd expect mine to use more oil.

The sled runs fine at higher RPM and more throttle opening. It's really hard and a little unsafe to ride when the trail is really rutted and rough and you want to go slow or while picking your way through the trees.

It worked fine up to about 300 miles, and now it has been a long time since it worked right, and its been at the dealer's for a couple of weeks while he works with Polaris and his own ideas and rides it when he can to test the latest idea. We could sure use your help in getting it back on our new 2 feet of snow!

Thanks for any ideas or experience you have on similar problems or testing ideas.

ShinyUp :banghead:

its caused by a lean condition and heat in the pipe. i have been fighting with a hanging idle and a lean condition at about 1/4 throttle. if i start it in the garage it will idle down, but once i ride for a little the idle hangs at about 24-2500. if i let it idle for a while it will eventually come back down. i have reset the throttle bodies to spec a half a dozen times now, hoping that it was something i did. i really have no explaination other than to tell you that its lean. if your dealer is competent he can reset the throttle body min air setting to effectively richen the mix. this is what seemed to correct the issue for me. it is not something that you want to get into unless you are a mechanically skilled individual. it is not a easy setup and can cause even more problems for you if not done right. i did however like the way it ran at wide open throttle! absolutely ripped!

Thanks for the idea WickedSwitch,

I don't know about the competence of the dealer, as this is the first time I've had to have dealer service. That's a whole other story! In general, I have found that Polaris dealers do not want to do warranty work, because Polaris does not pay them for all the time it takes to solve hard problems. Apparently, Polaris pays only for 1/2 hour to diagnose the problem, and a flat rate to make whatever repair is indicated. That's great if the cause is obvious, but the dealer looses time and money if the problem is hard or intermittent. Have any of you found a way to deal with this policy?

I talked to the service guy yesterday, after he'd ridden the sled over the weekend to see if the stator replacement fixed the problem (it didn't). He said that Polaris was now telling him to remove the fuel tank and check for known wire chafing problems. Since they had him take the tank off earlier for another reason, he's really annoyed that they did not have him check that known problem then, and is delaying doing the work till later this week. Meanwhile we have a major snow dump and are missing the fun.

Anyway it seems to me that this problem is different than your experience. This sled always starts easily, always idles at approximately 1,500, and always runs great above 5,000 RPM.

Sometimes, and ususally after many miles, it will get so that it "pops" between 4,000 RPM and 5,000 RPM. It seems like it just goes dead till the tach indicates 4,000 RPM, then refires and jumps up to 5,000 RPM. As I remeber the first time this was happening, the RPM range was higher, and the "going dead" would only happen every 5 or 10 seconds in that RPM range. Once it starts now, it's impossible to hold any RPM in the 4 - 5,000 range.

I am fairly competent as a troubleshooter and mechanic, but find that the information that Polaris provides in the Service Manual (PN 9919763) is poorly organized and not comprehensive. That's why I'm hoping someone had a similar problem and found the answer.

Thanks for your ideas and interest.

you said that the stator didnt fix it. hmm. well, i just started mine and it ran for a few minutes then all of the sudden it was like someone hit the kill switch. just like that, no power to anything. i almost have to beleive that the problems ive been having is realted to whatever just failed. i have nothing now, its like trying to start the sled with the key off.

ok, it starts again. went back out to see what it might be and it started right up. weird!

Have you pulled the tank and checked out the wiring. Have a look, especially at the capacitor connector. Also check the main connector from the stator for arcing or burning.

One thing about these kinds of issues is determining whether it's fuel or spark thats causing the problem. One has to develop a "feel" for it. An spark problem makes an engine die rapidly with a sound different then a fuel issue. Often a test run on a customers sled reveals much more than the customer ever could.
Has the dealer checked fuel pressure while the engine is misbehaving??
Has the TPS been checked for initial setup AND for continous reading throughout the throttle range? A bad connection in some part of the variable resistor could cause problem at a certain rpm.

Just a couple ideas to ask yer tech....