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High Altitude Carb Tuning

21231 Views 5 Replies 5 Participants Last post by  HMF-Exhausts
I am getting ready to go riding in soon to Utah. Obviously the elevation is a little higher than 500 feet. Do I need to be concerned with re-jetting my carburetor or should I be fine?
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A good rule of thumb is; if your going over 2000 ft +/- sea level then you need to adjust your carburetor to make sure you AFR (air / fuel ratio) is correct. Since higher altitudes have less air density (or simply put, less air) then you need less fuel. This is just the opposite for lower altitudes.

Most of the time for ever 2,000 - 2,500 feet above sea level you go you can expect to need to drop one jet size. You can also adjust the clip on your needle jet; or sometimes referred to as the metering rod (this usually only applies to aftermarket needle jets).

Keep in mind that a lot of other environmental changes affect carb tuning and performance such as temp. and humidity; so you may find yourself fiddling around with the tuning a bit to get it just right.
I agree with GW. The exact changes will be depending on your general elevation. For example, if you are going to be riding from 500 feet to 5000 feet or from 3000 feet to 10000 you will need to make a couple (or more) adjustments to maintain top performance throughout your ride. One way to address this issue is to install a Dial-A-Jet.

In using a DAJ, you will first want to ensure you have the settings just right for your normal riding conditions before taking-on any new riding conditions. This way you know what right feels like and can adjust the DAJ more effectively when the time comes. Also keep in mind, getting the DAJ tuned properly may require re-jetting at your normal riding elevation.

CLICK HERE for a review contributed by one of our members. A pretty good discussion follows the review as well.

Hope this helps some.
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Very good point Battlegun! I hadn't thought about the DAJ.
I would agree you just need to re adjust your carb if you are over 2000 ft +/- sea level. Lower than that no need at all.
I get allot of calls/emails about recalibrating the air fuel ratio for high elevation or extremely hot/cold ambient conditions.
So, to make everyones life easy I decided to post the E/T correcton factor chart.
Mind you, this is only a suggested baseline setting, fine tuning may be needed.

Example: We know the jet specs we offer are a good baseline for basic sea level and 55~65 degrees.
Lets use the Kawasaki Brute Force 750 as an example. We suggest a 155 front and 165 rear for the man jet.
Lets say we are going to ride at 6,500 feet at 68 degrees.
We know the 155/165 works well.
Looking at the chart:
We see the correction factors on the left side.
We see elevation in feet on the right side.
We see ambient temperature at the bottom.

Chose 6,500 feet then where it crosses ambient temperature (68 degrees) we get a correction factor of 0.94.
Since we know our main jets are 155/165 we multiply each x 0.94
We multiply 155 X .94 = 145.7 as a corrected main jet suggestion for the front carb. Round it off to a 145.
We multiply the 165 X .94 = 155 as a corrected main jet suggestion for the rear carb.

Note: the elevations are a bit hard to read.
They are top to bottom:
Sea level.
3,200 feet.
6,500 feet.
9,800 feet.

Another trick when you are climbing in elevation would be to remove the airbox lid as you get to the point where the machine is running poorly. This is due to the fact that as you climb in elevation there is less air, less air means more fuel which means the air fuel ratio will be too rich. Removing the airbox lid will allow more air thus leaning out the AFR. Much easier than trying to re jet.

Another trick for winter riding would be to remove that free flowing air filter (if you have one) and go back to the stocker.
Winter time low ambient temps make a machine run leaner. Removing that free flowing filter and switching back to the stock restricted one will allow less air and more fuel. Cold temps make the AFR leaner, so less air = more fuel thus a richer AFR.

It's THAT simple.


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