Three Stage A/F Adjustment
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Lead Driver
Joined: Mar 2008
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From: Near Los Angeles
Three Stage A/F Adjustment
For some time I've wanted to lean out my A/F ratio on my Holley 1848. Recently I had the air cleaner off and decided to tune it to the 12.6-12.8 ish idle mixture.
I got it easily, but when I put the a.cleaner on the mixture got rich again. I adjusted to the 12.6-12.8 that I wanted and closed the hood.
Yep, you guessed it. The mix changed again. So, I adjusted again! I chalk the changes up to air flow and air temp/density. I found it quite interesting. When I install a cool air air filter, I know I'll have to adjust it again.
I got it easily, but when I put the a.cleaner on the mixture got rich again. I adjusted to the 12.6-12.8 that I wanted and closed the hood.
Yep, you guessed it. The mix changed again. So, I adjusted again! I chalk the changes up to air flow and air temp/density. I found it quite interesting. When I install a cool air air filter, I know I'll have to adjust it again.
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Joined: Dec 2007
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From: Boise, Idaho
I've always seem to have to deal with this, too. Sometimes it'll idle at 11:1 and others at 13:1. It averages around 12 - 12.5:1, but there's simply no guarantee that it'll stay there. Even from stoplight to stoplight.
Cruise seems MUCH more stable though. If it's at 15:1 today, it'll be pretty close to 15:1 tomorrow.
Cruise seems MUCH more stable though. If it's at 15:1 today, it'll be pretty close to 15:1 tomorrow.
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Lead Driver
Joined: Mar 2008
Posts: 7,188
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From: Near Los Angeles
I believe a stable, steady reading depends on the engine compartment temperature. Hence your steady reading at cruise. Whereas at a light your engine compartment begins to warm up and the longer you are stationary the more stable your reading should become.
Of course if you have a cool air intake, disregard what I wrote.
Of course if you have a cool air intake, disregard what I wrote.
Lead Driver
Joined: Jul 2009
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From: Sheffield, AL
This thread shows why the engineers spent so much effort in designing vacuum and mechanical systems in an attempt to stabilize the air temperature inside the air filter as well as the intake manifold. 
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