| [GMCnet] Use of Carb at high elevation [message #340942] |
Tue, 12 February 2019 12:44  |
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Messages: 124
Registered: February 2019
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At higher elevations there is less oxygen so carbs set up for lower elevations will run rich at higher elevations with resulting lack of power.
If one was to begin operating at a constant higher elevation the carb jets should be replaced to maintain the proper air/fuel ratio. However if you are changing elevations while on a trip it would be quite a job to keep changing the jets.
I had lived in Santa Fe, NM for nineteen years at 7000 feet and would frequently take trips to lower elevations. Rather than constantly changing jets I would retard the timing at lower elevations. I found at high elevations I could get more power by advancing the timing. I could even set the distributor for perhaps 20 deg before top dead center and the engine would not ping. In order to make it easy to set the timing without using a timing light I attached a pointer to my distributor and painted marks on my intake manifold. I loosened the distributor just enough to be able to grasp it with my hands to turn it but still snug enough so that it would not turn itself when driving. This can be seen on the gmcmhphotos.com site.
I would reset the timing about every 2000 feet change in elevation.
You can see the distributor pointer at www.gmcmhphotos.com/photos/g3125-timing- marks-for-distributor.html
This also worked well with a tbi system which didn’t have a computer controlled distributor. After I modified my tbi system to a computer controlled distributor I no longer needed to manually change my distributor timing. This worked well for me for several years and provided more power and prevented pinging at lower elevations when traveling.
Emery Stora
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