First off I just want to say "Howdy" to all, now onto my problem. I have a brand new 2004 Sportsman 400 with less then 12 hours on it. The atv runs fine around home at about 700 feet but once I take it up to the mountains (5000-6000 feet), it runs like sh*t. The dealer told me it would have to be rejetted for altitude but I wonder if it really does or could there be other problems? Here is the story:
While up at about 5000-6000 feet the atv is hard to start, idles around 800 rpm and stalls occasionally. While pulling the slightest grade it sputters and will not go faster then 10 mph. At home, the atv is fine and idles around 1100 rpm. I can understand a lose of power at altitude but should it be this bad? I thought they were jetted from the factory up to 6000 feet? My friend has a three year old Magnum 350 and it runs like a champ, no problems, with the stock jetting, why is this? Just wondering what I need to do, I don't want to go to the dealer and just tell them to rejet when it could be something else. The dealer was quick to suggest rejetting over the phone and even told me I should have it jetted at a dealership that is at a similar altitude that I ride, does this sound correct? Maybe I am just paranoid, but it is strange to me how you spend all this money for a new atv and then have all these problems. Any help, suggestions, ideas, what I should do, would be greatly appreciated. I have no mods as of yet. I look forward to any replies, thanks.

 

Hey,
I am from reno and you are describing my sp400 to a tee!!! My bike is in the shop right now getting a new master cylinder put on so I called the tech and asked what he thought. He told me that the bikes were jetted to around 5000ft max but I ride between 4500 at home and 7500 on the trails. His first sugestion was to try a hi flo air filter (k&n) that acts like a 1/2 jet smaller and if this didn't help enough to go to a smaller jet. He also said to be careful if you jet down then go back to a lower elev. that you can burn your engine up because it runs to lean. I should get the bike back tomorow and will put the filter right on and see how it goes!
Hope this helps a little
Chris

 

I would agree 100% with your dealer. Most atv's are jetted rich from the factory and as you go to a higher altitude, you need to jet down. The air is thinner up high, so you have all this gas going in and not alot of air, so it will run like crap until you jet down. If you do alot of elevation changes, you can look into getting a Dial-A-Jet Kit that makes it much simpler to adjust the jetting.

 

Thanks for the info guys, I hope it will be as easy as jetting. I have an appointment with the dealership on Wednesday so we shall see what they say. I just find it strange that my friends three year old Polaris 350 didn't need any tuning at all yet runs fine. You would think a brand new 2004 would be just fine?

 

Have a 2004 Sp 400 with 112 miles on it and I live @ 7,100' elevation. here is what I have in it.

I pulled the stock jetting out (145) and went to a 160 main...
I pulled the stock B10H weights and went to a White ( W10H) weights...Runs better BUT>>>>>>>>>
Going to R10H weights as the 400 want's more RPM At wide open....... I also pulled the Green/Blue primary spring out, and went to a straight green spring, from Polaris.

Keep in mind that I live right where you ride in the mountains.........and I go up as High as 9,000' elevation..

I found out that the 400 (OPERATING-RPM's are 6300) so you need to jet and clutch around that information.
With you New machine providing a tach, read it and clutch to it.....

With the jetting and cluthing I have right now, I'm only running 5,500 RPM Wide Open, with a 48MPH speed...
won't come close to my 500HO or the 'OLE 400 xplorer, but the 400 Sportsman is twice as strong as it was when I received it....and it was Jetted and clutch for my elevation...........RIGHT!!!![img]i/expressions/face-icon-small-disgusted.gif[/img]

If you need help Just ask, as I'm not done tinkering with it just yet.....other wise I'm still stock-even the air cleaner, need to get the money out of stock air cleaner first........

 

Thnaks SageCrusher. great information there. The bike is currently at the dealer so I need to see what they do with the jetting first but it sounds like you got it down right. I am having to wait a week and a half to get the bike because the brake master cylinder needs to be replaced under warranty, it was leaking everywhere. Sure hope its not a lemon! I will report back as soon as I can test the thing out up in the mountains.

 

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I had the same problem with my 2001 Sportsman 400. Got it re-jetted, and works a little better. You'll notice that there will be some increase in power and better idle. Just a heads up though, when you are in the high altitudes and you shut off your machine, it may struggle to get started again ( The starter just cranks a little longer to start the motor). But then again, all machines are different. Hope everything turned out for the best.