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Discussion Starter · #1 ·
First time out in our 21 KRX to Colorado high country. The engine is very sluggish above 9000 ft and it gets much worst on up. Is there a fuel controller or reflash that will help!!
 

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Guess I must just not know any better since I live in Colorado and all my riding is from 8,500' and up. lol Mine runs fine at high elevations.

4509
 

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Welcome to the forum. Power loss at altitude is about 3% per 1000ft. So at 9000ft you have lost 27% of your HP or about 30 HP. A tune will only gain back 3-4 HP at that altitude. The only real solution is forced induction.
 

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I found out while riding around Lake City and Silverton that any time I got real high I needed to loosen the gas cap and let the tank vent. It even got to the point that my riding buddies would do it for if they were close when we stopped. It sounded like a jet engine when it was cracked open. Pretty sure this will affect performance! There is a cheap cure available, a rollover vent valve installed in the tank vent line seems to do the trick. Ordering mine Monday.
 

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Gas cap is likely just a one off issue…

At those kind of elevations is where a properly tuned turbo car shines. With NA there is not a lot you can do to overcome the loss in air density. It is what it is. With a turbo you can lean on it a little harder (in the tune) to compensate for loss in air density.
 

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The gas tank vent problem is well known even at low altitudes. There's a Facebook forum for the KRX and a large group of the members are southeastern trail riders. Hatfield McCoy, Black Mountain, and many others. That was how I learned about it. I am surprised that I haven't seen it mentioned here.
 

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The gas tank vent problem is well known even at low altitudes. There's a Facebook forum for the KRX and a large group of the members are southeastern trail riders. Hatfield McCoy, Black Mountain, and many others. That was how I learned about it. I am surprised that I haven't seen it mentioned here.
I think a lot of us that have done the mod take it for granted and just forget to mention it.
 

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First time out in our 21 KRX to Colorado high country. The engine is very sluggish above 9000 ft and it gets much worst on up. Is there a fuel controller or reflash that will help!!
Wow I was just on a 122 mile trek with 1/3 of it about 9000 feet and the highest at 11,672. In general no problems.. actually up to 60 MPH above 11,000 feet!
 

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Discussion Starter · #13 ·
I have ordered the rollover valve and will try it. My KRX behaves like it is in low power mode from 9000 and up. It takes half the throttle to make the machine respond and then it lurks ahead and if you let it drop below 3500 rpm it bogs and loses power quickly. If you gas it it goes at it again but slowing is the same it tries to die. As you descend the performance picks up again to normal. I understand the effects of alt. on natural aspirated engines but this is much worse. Any advise?
 

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At that elevation in Colorado you always have to worry about marmots crawling in and messing with your throttle linkage.just like the beavers in the yellawood commercials:oops:
To be serious which to difficult for me at times. Are you visiting from a lower altitude or purchased the krx in another state. First reason up here for poor performance is lack of oxygen . Fuel air adjustment ,air filter blockage,fuel delivery problem,plugs. Haven't had any problem with my krx at high altitude, other than waiting on razors,can am's to get out of the way. (Just kidding) good luck let us know if you do the tank mod and if it makes a difference. If it does I'll order mine just in case.
 

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I am a Coloradoan that has freinds from Joplin Missouri that come here to ride the high country and their machines have had issues at times. I dont know if its the difference in fuels that are delivered to different regions (1000ft elevation vs 5000+) but sometimes their machines act like they are vapor locking or a bad fuel pump, they wont idle, loss of power and just run crappy. One thing for sure, fuel will boil easier at these elevations vs Missouri elevations.
We have had good response by treating the fuel with marvel mystery oil to raise the boiling temp, this has even helped when it didnt appear warm enough to cause vapor locking. The added benefit is upper cylinder and valve lubrication.
Ive never had this problem, but all my fuel is purchased here. These symptoms have happened in most of the machines they've hauled out here at on time or another and one of the rzrs sturns on the check engine light whenever he's here.
Dont know where your fuel is coming from, but I am curious if its from low elevation country.
 

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It’s an old thread but I’m in it so I’ll add that the rollover valve mod is probably BS. Didn’t do crap for me but I’m East Coast under 2500 feet.
 

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I can imagine circumstances where a positively pressurized fuel tank would reduce pump cavitation potential and increase flow by increasing suction side pressure. Wonder if it is designed that way?
 

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I can imagine circumstances where a positively pressurized fuel tank would reduce pump cavitation potential and increase flow by increasing suction side pressure. Wonder if it is designed that way?
I don't think I buy that. Maybe in the days of mechanical fuel pumps mounted on the engine, but not with electric pumps sitting submerged in the tank. A little pressure won't hurt anything, but some of these are excessive. Probably even more so here in Colorado. You fill up at home in 50 degree weather at 5,300'. You get out and ride and end up over 11,000' and near 80 degrees (plus the heat from the coolant lines that split the fuel tank). The combination of heat and altitude gain builds tremendous pressure in the tank. Same is true with my tires. They will build as much as 4-5 psi in those same situations. Doesn't sound like much until you consider that's nearly a 50% increase.
 
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