Mathews Inc.
High Altitude Gas
Elk
Contributors to this thread:
Aspen Ghost 10-Aug-17
drycreek 10-Aug-17
jordanathome 10-Aug-17
Tdiesel 10-Aug-17
coelker 10-Aug-17
Jaquomo 10-Aug-17
jordanathome 11-Aug-17
midwest 11-Aug-17
Surfbow 11-Aug-17
EmbryO-klahoma 11-Aug-17
ASCTLC 11-Aug-17
Teeton 11-Aug-17
ASCTLC 11-Aug-17
Fulldraw1972 11-Aug-17
midwest 11-Aug-17
EmbryO-klahoma 11-Aug-17
Alaska at heart 11-Aug-17
deadeye 11-Aug-17
ASCTLC 11-Aug-17
Native Okie 11-Aug-17
Ski & Skin 11-Aug-17
From: Aspen Ghost
10-Aug-17
My little Honda CT110 works well for me on the plains. But at around 9000 ft it tended to lug going up steep climbs to the point of stalling out. I just put in a high altitude jet. Hopefully that will help.

I've always brought a 5 gallon tank of gas from home but I see that all the gas stations in the mountains sell a lower octane gas and that is recommended for most vehicles at higher altitude. Should I buy this lower octane gas for my CT110 instead of bringing flat lander gas?

How about gas for generators and chain saws? Should I use the lower octane "mountain" gas or is flatlander gas ok?

From: drycreek
10-Aug-17
And here I was already feeling sorry for your tent mates.........

From: jordanathome
10-Aug-17
I think the gas from home is fine. The issue really is leaning out the carb which can be bad but your rejet job should avoid that problem.

From: Tdiesel
10-Aug-17
Your gas from home is fine at higher altitude we have a harder time detonating gasoline thus we can run a lower octane your problem is the air/fuel mixture. it is used to having a lot more air so it can add x amount of fuel up in the mountains you are running on a small percentage of the air so you need a smaller amount of fuel to make it correct air/fuel mixture. the jet will help just depending on the elevation it may or may not be enough. on my snowmobile at 12000 ft I run significantly smaller than the recommended high altitude jet which is good for about 9000 ft generally

From: coelker
10-Aug-17
Gas is fine. Octane ratings are simply the gases ability to resist detonation from pressure. The different levels of octane are designed to perform in engines with different compression ratios. Anytime you compress a liquid or gas you increase the temperature. In a high compression engine you can compress a lower octane gas enough to predetonate it causing engine knock and possible damage.

Since most small engines are low compression they can run a lower octane gas. So your generator should fine on regular gas.

The gas industry has made a fool out of most consumers. They decided that regular mid grade and premium should be used to identify gas octane ratings. In the vast majority of engines regular works just fine. It is only performance engines that require higher octane levels.

Now to your issue. Your compressor runs crappy at elevation due to a poor fuel air mixture. Specificatlly lack of Oxygen. The carb is tuned to have a certain air fuel ratio. When at home you have X amount of O2 and as such the carb supplies enough fuel for X. At elevation you have significantly less O2 and supplying the same amount of fuel leads to an engine running rich and poorly. Changing the jet should have slightly decreased the fuel supply to match the decreased O2.

I find that many high country hunters do not address this at all. They do not understand the issue etc.

My carb on my jeep runs great from 4,000 to 8,000 feet. Above 8,000 I have to adjust it. Below 4,000 I adjust again.

In modern vehicles we use MAP sensors, Masan airflow sensors and Oxygen sensors to automatically adjust air fuel ration.

From: Jaquomo
10-Aug-17
X2 coelker. Every year I have to counsel guys who have generator issues at altitude. They are jetted for sea level and don't perform well higher. Where I live at 8500 is a LOT different than the flatlands. Even with a high altitude jet the wattage output is reduced. Honda publishes a great power-altitude curve chart for different jets that really illustrates the difference..

From: jordanathome
11-Aug-17
Best threat title EVER

From: midwest
11-Aug-17
Ditto drycreek...I thought it was another chili mac thread!

From: Surfbow
11-Aug-17
This is funny, while scouting last weekend we watched a guy try to run this goofy all-terrain mini bike up to about 12,000 feet. On our way down we pulled over to help him. He was trying to coast it down the hill, which wasn't working too well because of some weird clutch/belt drive system it uses. He had no idea why it wasn't running right. I told him it wasn't jetted for that altitude, and he looked at me like I was some kind of fool and told me "Well, it ran fine when I bought it a couple weeks ago..."

11-Aug-17
Thought for sure Aaron Johnson was going to be the OP. :)

From: ASCTLC
11-Aug-17
Tdiesel and coelker have it right, you need to lean out the mixture as you increase elevation for the reasons they explain. But I'll forewarn you, you need to rejet to richen your mixture again when you return to lower elevations before you just go running your equipment again.

Honda makes figuring out the appropriate jet size easy for EU2000 generators (0-5k, 4k-7k, 6k-10k, and last is 9k-15k) but for your ATV I don't know what the elevation ranges/jet size they suggest. You'll have to find it on line or at an ATV shop that may have that information.

95% of my gen use is from 7k-10k so that's what I jet for. But if I went down in elevation to camp I'd rejet to protect my equipment more so than to improve performance and efficiency.

While a too rich mixture will result in lousy performance and efficiency, too lean risks actual damage. Too lean often results in increased combustion chamber temperatures and are even known to melt pistons in the worst cases.

Andy

From: Teeton
11-Aug-17
What everyone said above..

If your atv stops working because of running rich it's most likely because the spark plug got fouled. Plugs are cheap. Take a few extra plugs and the tools to change it. Keep the plugs/tools with you (in atv) and wrap the new plugs so that the gap don't get knocked off driving the atv around. The guy above that had his bike stop I bet his plug got fouled.

E ven if your atv work great with your new jet you most likely see a decrease in power maybe up to 30%..

Ed

From: ASCTLC
11-Aug-17
And re: octane ratings, as coelker points out it's been a mess of understanding what it actually means. It is a rating of predetonation resistance. Where some have found a performance difference is for those motors that actually have a knock sensor that allows the PCM (the vehicles computer) to retard timing to mitigate the knocking caused by detonation. Retarded too much usually results in a reduction of engine performance. Not all engines have this knock sensor, but the average public has no idea of this cause and effect. I believe many high performance engines (via high compression combustion chambers) typically use a knock sensor because those higher pressures are likely to cause and suffer from detonation more than a typical compression ratio engine.

It's a deep subject but know even then all 87 octane is not the same, it's (R+M)/2. That's (Researched + Motor)/2. There's the calculated octane level ('researched') and there's actual tested levels ('motor' on a specifically calibrated test motor for that purpose). Some engines do better with higher theoretical octanes (research calculated) and some do better with motor determined octane ratings. You won't know this because fuel mfrs only advise the octane rating is a calculation of the (R+M)/2 and close enough for 95% of the general population.

I run the lowest octane I can unless or until I can notice detonation occurring on those blistering hot summer days under a lugging heavy load on the engine. Then I buy a higher octane level fuel until my use is no longer that stressful on the engine.

From: Fulldraw1972
11-Aug-17

Fulldraw1972's embedded Photo
Fulldraw1972's embedded Photo
Did someone say gas and another say chili mac?

I got it covered :)

From: midwest
11-Aug-17
EmbryO.....is there something I need to be warned about???

11-Aug-17
You have been warned. That's all I'm saying. :)

11-Aug-17
Quite disappointed that this thread was about running an ATV at elevation......that is all I am saying on the matter. 8^p

From: deadeye
11-Aug-17
older jetted carbs can be fixed very easily by buying a larger air jet not going smaller on the main jet. Going smaller on the main jet will only help some but you will still have less power. Just go bigger on the air jet .

From: ASCTLC
11-Aug-17
Until he takes his ATV airborn we can only discuss it relative to elevation. Now, if he runs it off a cliff in to mid air, we can expand the discussion to how it's then running at altitude (at which point I don't think that's going to be a primary concern then) :D

From: Native Okie
11-Aug-17
Easy fellas. It's not that bad ;^)

From: Ski & Skin
11-Aug-17
Only when I eat mountain house!!!! The i have lots, enough to push me up the hill with each step!

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