I have just spent the last five or so years troubleshooting seeming never-ending engine problems on my 2001 Polaris Sportsman 500 HO. Now that I finally got it running properly I thought I’d write up what I found and maybe it can help others.

In summary, this is what happened:

1 - Failure of the Electronic Throttle Control causing a loss of spark
2 - Failure of the oil pump causing destroyed piston and bearings
3 - Mismatch between the stator and CDI causing a misfire at high RPMs
4 - Improper position of o-ring on carburetor fuel screw causing poor idle
5 - Obstruction of air box snorkel causing poor high RPM performance

I bought the Polaris used in November 2007. I got it for it’s snowplow for my winters in Salt Lake City, Utah, and for mountain and desert riding in the summer. I also have two Honda ATVs. I have some experience with automobile engine repair. I’m no expert, but I’m not totally incompetent either - although it may seem like it after reading all this.

My Polaris ran fine for a year and a half. Then one day minutes from my home the engine just quit. Back in the garage I checked for the three essentials and found it had no spark. Sometimes it would have spark for one or two cycles, but then nothing. So I tested and replaced ignition elements one at a time. Still no success, and the ATV sat for most of a year or so after that.

I eventually took it to the local college where they have course in ATV/snowmobile engine repair. It turned out to be the electronic throttle control was way out of adjustment, cutting off my spark. They did what I asked and got a spark.

But once back in my garage, even though it had a spark it still would not run. The college instructor suggested a former student who now had his own shop. He tore the top end apart and found severe damage from lack of oil. So the ATV sat for three years before I decided to work on it again.

This time I bought a used engine from a 2000 Sportsman 500 HO and swapped it out with my dead one. It started up and seemed to run great. I’m not a hard rider so I rarely max out my engine. But on one outing it started to rain, so I pushed it to get back to camp. It really bogged at high RPMs.

When I got home I tore in to it to see why it was bogging. I checked everything - except the actual problem which turned out to be a mismatch between the 2001 CDI on the original machine and the 2000 stator on the replacement engine. This caused a miss at high RPM.

But I didn’t know that. So I checked the exhaust lobe on the cam, rebuilt the carburetor two times, checked ignition timing more times than I can count, cleaned out fuel lines, the fuel pump, and the gas tank, replaced old fuel, and did everything I could think of before taking it to a mechanic nearby to help find the problem. He checked all I had done, and also put a timing light on it at high RPM. He saw the missing sparks and also noticed an unaccounted for green wire from the stator that had no place to go on the CDI, and suggested I look in to that.

So I swapped the stator for the other one from the 2001 engine, and then it ran great at high RPM.

But now it idled poorly. I had to keep the choke on for the engine to idle, even when the engine was hot. And if I disengaged the choke it would run great at high RPM but then die at idle. Frustrated, I went back to the carburetor.

I did a very conscientious carburetor rebuild this time. I noticed that the o-ring on carburetor fuel screw was not on in the right order. I corrected the problem and finally the ATV idled properly.

But now it was bogging again at high RPM - actually killing the engine when I gave it throttle! I was pulling my hair out by now. This Polaris was cursed. That had to be it.

I remember from earlier reading that other riders said messing with the air box cover produced some changes affecting high RPM performance, so I removed the air box cover - and the engine almost died. I put it back on, cracked it open just a little bit and the engine revved clean up to the high RPMs just like it was supposed to.

It turns out that with all my messing with body panels and stuff, the foam support for the snorkel and belt vent tube had been jammed up under the gas tank, out of view. When I put the air box snorkel up there, the foam would cover the open end just like someone being suffocated. It let enough air through for idle, but at full throttle it starved the engine for air. I relocated the foam support, and the engine now runs like it was designed to.

So now it’s February 2015. I’ve had the Polaris seven years but only had the use of it for a total of maybe two. It runs pretty good now. I’m tweaking the idle and may make other mods, but at this point if it acts up again I think I’m going to go out of my mind!

 

Wow!
You had a more than usual amount of hair pulling problems. I own a 2001 500 HO also and only had minor issues so far. (Knock on wood) I find the old ones are more reliable than the newer ones too.
I hope you can enjoy this rugged bike you have now. With regular preventative maintenance , they should last a long time. They are a blast to drive....
Enjoy your ride!

 

1 - Failure of the Electronic Throttle Control causing a loss of spark
2 - Failure of the oil pump causing destroyed piston and bearings
3 - Mismatch between the stator and CDI causing a misfire at high RPMs
4 - Improper position of o-ring on carburetor fuel screw causing poor idle
5 - Obstruction of air box snorkel causing poor high RPM performance

Granted some of this was unfortunate such as the oil pump failure,But when it lost spark the first time and was due to the throttle cable which was out of adjustment,the owners manual or service manual addresses this as to how much slack is needed for the etc switch.I had dozens of people that came to the shop for dieing problems,no idle and I fixed them in back of trailers or pickup trucks. All they had to do was look at the owners manuals.Plus letting it sit for a year before this was addressed?? And yes electronics aren't always compatible between year models. All the parts sites list the correct component for that year model such as the cdi problem you had.The 2000 Sportsman 500 engine had 3 cdi options along with 3 stator options depending on build date(build date available from the 17 digit vin #) Plus the 2001 Sportsman you have is the HO version,different cam and electronics as you've found out. The air box cover has to be used on the atv or they wouldn't have installed it in the first place. They would run too lean and bog without it, granted the foam collar could creep up on the snorkel on these models and block air input,but should have been something easily found. Being a used machine,length of time between repairing may have had played a big part in this whole scenario. Not trying to criticize,but a lot of problems could simply have been avoided by the owners manual and the service manual.If it acts up again I'd either get a mountain bike or a horse.All you have to do is to feed him and clean up behind him.Just my on this but hope it holds up for you and the problems are all behind you..

 

My god I think I want to sell while the getting is good. LOL

I never had any of those but here are mine , The no spark do to the throttle was easy for me since I seen it many times and it was a 15 second adjustment.

1) It would start with pull cord but not electric
Fix-It was a dirty pulse coil I just had to clean it, dirty water gets by the pull rope handle and inside the recoil cover.

2) Electric starter quit and just "Clicked"
Fix - took starter apart and found one of the brushes was dirty and sticking ,so I just cleaned it up and it moved free once more.

3) Water was getting into the belt housing.
Fix- Turned out not to be the belt cover seal but a round seal behind the Primary clutch which requires the clutch to come off to be replace.

4) Ripped rear CV boot, really does not count since it Happens to all ATVs.

5) Speedo quit working but AWD still worked and Hour meter.
Fix-Turned out to be a wheel sensor(Hall Effect) I just left it as is since the speedo is so fogged up I can't see it anyway.

6) Fan died and dealer wanted $350 for a new one.
Fix-Found out "Spal" of Italy makes the fan and went on their web sight and bought one off them directly for $80 delivered (Talk about mark up). Installation was 20min.
Manual wanted me to take the whole front end apart to change the fan.

Had the ATV for 7years and all problems where small and cheap to fix so I can,t say it's to bad.

 

Welcome to the forum. thanks for sharing your experience.