# High altitude adjustment



## GoBlowSnow (Sep 4, 2015)

At what altitude do they recommend re-jetting for high altitude? Is that all that is needed for high altitude use? Aside from having to use lower octane as well.


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## stromr (Jul 20, 2016)

When I used to travel around the lower 48 states to race motorcycles, Honda used to tell us horsepower will decrease 3.5% for every 1,000' you go up in elevation from your previous location. Sometimes from one race meeting to another the elevation didn't change but a couple hundred feet. Still we fine tuned the bikes. Only time I remember rejetting the pit bike and the generator was when we went to Pikes Peak, Colorado. I'd say 0-5000 on a small engine will be the same, over 5000, rejet. Same guidelines you use for baking a cake, usage of baking powder, sugar and oven temperature are reduced.


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## [email protected] (Nov 21, 2011)

GoBlowSnow said:


> At what altitude do they recommend re-jetting for high altitude? Is that all that is needed for high altitude use? Aside from having to use lower octane as well.


You may need to swap out the jet, but nothing else really needed for a snowblower at higher altitudes (5,000 ft. is a good starting point). 

A smaller jet compensates for the reduced air/oxygen at higher elevations, and keeps the ratio of air-to-fuel correct. Too large a jet with reduced air/oxygen may result in a rich-running condition, which may be observed as black/blue smoke from the exhaust (incomplete combustion). 

I think an engine rated to run on XX octane should stick with XX octane, regardless of altitude. If you're using a higher octane fuel than specified by the manual, it is likely not necessary.


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## russkat (Feb 25, 2015)

I've not had a problem with standard jets from Morrison on down to Denver metro, but certainly had to rejet when l lived up in Breckenridge and the elevation at my house was approx 10,300 ft. Those were fun days !

Some manufacturers suggest over 5,000 ft, some say over 6,500 ft, and I had a boat a while back that suggested rejetting over 7,000 ft.


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## GoBlowSnow (Sep 4, 2015)

I'm at right about 6000ft I've noticed some carbs run ok and yet others seem questionable? That's why I was asking. They can be brand new or used and rebuilt and get a proper cleaning to ensure all passages and ports are clean and open yet I can't quite seem to get it to run smooth where as others will be great.


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## russkat (Feb 25, 2015)

I had that issue with my Ingersoll loader with 20hp Kohler twin.

I had the original carb apart over a dozen times and it never did run 100%, I finally bought a new factory carb and it has run perfect for the last 2 1/2 years. 
Anymore, if a rebuild kit is close to half the cost of a new carb, I'll spring for the new carb and keep the old for spare parts. 
I'm sure the jet can't be very pricey, so I'd just do it and see if it cures the problem.


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## stromr (Jul 20, 2016)

*this will help...*

I forgot I had this picture. Blow it up big enough and you'll see there is a wide range of color the sparkplug can look like and still be OK. We always used to say if the plug looks like coffee with cream it's good! Some people like their "coffee" lighter than others. I'd err on the darker side because the lighter it is the hotter it runs and the faster the engine wears. Too light (lean) a mixture and things get hot and you hole pistons and burn valves.


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