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I just got back from a elk hunt out west. I used my Grizzly 550 on the hunt in altitudes 7000-9000 feet. After running a few miles it would start missing and stall out. I would turn the key off and back on and it would start fine like nothing was wrong. When I would pick up speed it would start to do it again. After the 1st day of this I changed the spark plug. It was dry. The 2nd morning I probably traveled 8 miles before it did it again. After it started it was a struggle getting it back to camp. All of this didn't start until the 3rd day I was out there. Last year it didn't act up the entire week I was there. If it matters the only thing I burn is 91 premium non ethanol fuel. Has anyone else dealt with this?
 

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Welcome from Colorado.
Low compression engines don't need high octane fuel.
Most around here run e-85 with no problem, and some add a little injector cleaner to the gas every now and then.
There is very little humidity here so moisture in the gas is not a problem like in other areas.
 

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I just got back from Utah and my 2012 550 didn't run right above 10000 ft until the second day it finally straightened out after I run all of the fuel I took from tn and filled up with 85 octane
 

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Welcome from Colorado.
Low compression engines don't need high octane fuel.
Most around here run e-85 with no problem, and some add a little injector cleaner to the gas every now and then.
There is very little humidity here so moisture in the gas is not a problem like in other areas.
Especially at High Altitudes.

Try the lower octane fuel and see if it makes a difference, I bet it will.

DEWFPO
 

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Thanks to all! Are you burning 85 to 87 fuel with ethanol? Around here the only gas without is 91 octane. What stinks is I live at 1500 feet so I don't get a chance to test it until I go again. I just don't want to ruin another trip!
 

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Doesn't hurt to find non-ethanol fuel when you can. But you're just wasting money, and potentially making your machine run poorer, if you get the higher octane fuel just to get ethanol-free gas.
When I find a station with ethanol-free 87, I buy it. Otherwise I fill up with the 87 from any name brand fuel station. Your machine was designed for it.
 

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Thanks to all! Are you burning 85 to 87 fuel with ethanol? Around here the only gas without is 91 octane. What stinks is I live at 1500 feet so I don't get a chance to test it until I go again. I just don't want to ruin another trip!
I live on the western slope of Colorado and 85 octane is our lowest option, then 87 and 91.
To get corn free gas I have to travel @100 miles one way, so I don't.
I suggest you bring your grizz low on fuel to Colorado and try a tank from here, and bring along a couple of jugs of your stuff from home.
 
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Thanks to all! Are you burning 85 to 87 fuel with ethanol? Around here the only gas without is 91 octane. What stinks is I live at 1500 feet so I don't get a chance to test it until I go again. I just don't want to ruin another trip!
I'm using 85 octane 10% ethanol.

DEWFPO
 

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Thanks to all! Are you burning 85 to 87 fuel with ethanol? Around here the only gas without is 91 octane. What stinks is I live at 1500 feet so I don't get a chance to test it until I go again. I just don't want to ruin another trip!
You can run ethanol fuel no issue. Contrary to popular belief, it doesn't hurt to burn ethanol in your ATV. Running it is never an issue. It's the storage of it that's the problem. You can't store ethanol fuels for long as they break down.

Run 87 or 85 octane in your bike at high elevations and you will not have the running issues you had. Ridgway is the guy that knows all about that with the years and thousands of miles of experience to back it up.
Once your done your trip, if you still have ethanol fuel in your tank, drain it out or ride the bike long enough to use it up. If you have any gas cans with ethanol fuel in them, just put it in your car/truck and use it up.
 

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Did you find the problem? If not try cracking the fuel cap as it's doing it to see if you have a vacuum lock, water in the float bowl can be a pain in the butt, a blocked fuel filter in the tank or the line will give you the same problem, another issue can be bad fuel that has lost it's octane rating(old/stored fuel)
 

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WOW! How the octane/corn conversation has changed! I run 87 with corn in everything..except my skidsteer. I have never had any fuel related problems.
There is millions of pages of research out there comparing the ± of corn, no corn, high octane, lower octane. Somebody been reading?

Using a slower burning (91) can only add to the problem at higher altitudes.

FYI... The refineries add butane and other chemicals to the gas for winter use as it make the fuel vaporize easier. Use up all your winter blend fuel before summer and don't take winter blend fuel to high altitudes.

This guy may not be a scientist however he is relaying info that I have read other technical papers.
notes-from-the-field-ethanol-vapor-lock-and-other-gas-woes
 

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There is another part to the low performance problem riding at higher elevations on a grizz., and that is the stock bike set-up sucks for those wanting peak performance. The aspect that is most responsible for this weak bike performance is the factory C.V.T. ratio.
At sea level there is enough air for the gas added for the throttle input for moderate riding, but at altitude as you apply more thumb for increased air to the engine there is also more gas added which is not needed.
To help counteract these problems I cut holes in the air box lid for more air volume than could pass through the stock snorkel,
And....learned to raise the pulley ratio which multiplies the torque produced by the engine with less thumb input.
Most of the miles on my 660 have been above 9,000 ft. and much of that has been above 10,000 ft. which in the summer means I'm down 40% or more on oxygen to the engine, but not down on gas delivered to the engine for any thumb position.
After 1000 miles I added taller tires and that magnified the problem until I had to start changing things, and that's when I started experimenting with C.V.T. mods and air box lid mods, listed in my signature, that work for this area.
Old time members have probably seen these, but here you can listen to the engine responses after modifications were made to free up the engine,
and here is more video carrying speed between 9,000 and 11,000 ft. The camera for this video was mounted on the roller fair lead so there is a rattling sound from the hook.
This video is above tree line and tops out above 13,000 ft.
all on 85 octane corn.
 

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Discussion Starter #13
Thanks again to all especially Ridgeway. Hopefully the right fuel will fix the problem. Nice country in the videos. Thanks again!
 

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Ridgway, enjoyed the vids. I never appreciated the pulling power of your Grizz setup until I experienced the high altitude drop effects on power first hand. I am sitting here laughing remembering the time at the cattle pen, my friend Jason, going to ride a wheelie at the start of the ride and about fell over the front of the machine because nothing happened, we both had a good laugh on that one.


I don’t think that this was mentioned, but make sure air cleaner is clean, and service daily out there, very dusty at times.
 
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Ridgway, enjoyed the vids. I never appreciated the pulling power of your Grizz setup until I experienced the high altitude drop effects on power first hand. I am sitting here laughing remembering the time at the cattle pen, my friend Jason, going to ride a wheelie at the start of the ride and about fell over the front of the machine because nothing happened, we both had a good laugh on that one.


I don’t think that this was mentioned, but make sure air cleaner is clean, and service daily out there, very dusty at times.
That was his first high altitude lesson, and by the look in his eyes, he wished he had a bigger machine.
His other lesson with the Honda 500 was to get a good run approaching uphill pulls, and not to rely on big torque to get to the top. In this area 13,000 ft. reduces engine output by 52% in the summer.
You don't want to retard the burn rate of the gas up here, you want it to ignite quickly.
 
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