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Old 05-31-2019, 07:01 AM   #21
flatford8
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Default Re: Air/Fuel Meter/gauge

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One of the reasons the opinions vary WIDELY on what the A/F should be set to is the variances between different meters. There is also the fact that differing engine systems can dictate the requirement for different mixtures. I have tested several brands of A/F meters under the same conditions and found that the owner should plan to experiment beyond what the meter is indicating.
Some of the “tuning” involves making the engine run right, not just satisfying the meter,..... correct?.....Mark
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Old 05-31-2019, 01:27 PM   #22
Ross F-1
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Default Re: Air/Fuel Meter/gauge

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One of the reasons the opinions vary WIDELY on what the A/F should be set to is the variances between different meters. There is also the fact that differing engine systems can dictate the requirement for different mixtures. I have tested several brands of A/F meters under the same conditions and found that the owner should plan to experiment beyond what the meter is indicating.
I installed an Innovate AFM on my truck, used it to tune my Holley 94. Decided I was done with it, so I sold it. Then I switched to a Rochester 2G, so I bought another one. There is about a 1.0 difference between the two units. Interestingly, both show 12.5:1 when the PV's are clearly open.

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Some of the “tuning” involves making the engine run right, not just satisfying the meter,..... correct?.....Mark
My engine runs like crap if I try to get above 13:1 at or just above idle. I've read where some get their engines to show 14's at idle, just not in the cards for mine. The difference in gas consumption just can't be significant, the difference in driveability is huge.
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Old 05-31-2019, 01:55 PM   #23
51 MERC-CT
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Default Re: Air/Fuel Meter/gauge

Trying to achieve those readings at idle seems like too lean to me.
What are your cruise speed readings?
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Old 05-31-2019, 02:42 PM   #24
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Default Re: Air/Fuel Meter/gauge

At a steady cruise, 45+, mid-to-high 14's. I could do better but I live at 5300' altitude, but have jets that allow me to get down to the lowlands without hitting 17's. Also, pushing a truck thru the air takes a lot more HP at cruise than a smoother car. The drag coefficient for a '52 is about the same as a barn door.
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Old 05-31-2019, 03:14 PM   #25
51 MERC-CT
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Default Re: Air/Fuel Meter/gauge

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At a steady cruise, 45+, mid-to-high 14's. I could do better but I live at 5300' altitude, but have jets that allow me to get down to the lowlands without hitting 17's. Also, pushing a truck thru the air takes a lot more HP at cruise than a smoother car. The drag coefficient for a '52 is about the same as a barn door.
Ya' I can see where altitude change could present a problem.
Would be nice to adapt an aircraft carb. with variable mixture control on the dash but those are for the most part, up draft carbs.
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Old 05-31-2019, 03:22 PM   #26
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Default Re: Air/Fuel Meter/gauge

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Ya' I can see where altitude change could present a problem.
Would be nice to adapt an aircraft carb. with variable mixture control on the dash but those are for the most part, up draft carbs.
Then you need the instrumentation to adjust it!
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Old 05-31-2019, 03:32 PM   #27
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Default Re: Air/Fuel Meter/gauge

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Then you need the instrumentation to adjust it!
Not on the ones I had, just a mixture control on the instrument panel to adjust for altitude.
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Old 05-31-2019, 03:38 PM   #28
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Default Re: Air/Fuel Meter/gauge

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Not on the ones I had, just a mixture control on the instrument panel to adjust for altitude.
That is interesting, so you adjust it by ear? Everything I have flown had EGT gauges at least.
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Old 05-31-2019, 06:36 PM   #29
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Default Re: Air/Fuel Meter/gauge

I am in mid-central Minnesota at a bit above 1000' elevation. I have an AEM gauge on my test stand. From experience, while a flathead will run at the desired 14-15:1 at speed, they tend to idle best at about 10:1. I consider it to be normal, and have convinced myself to live with it.
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Old 05-31-2019, 10:15 PM   #30
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Default Re: Air/Fuel Meter/gauge

A lean mixture needs more advance in cruise, and there only distributor that can providing that is the SBC along with the right advance under pow.. It get kinda tricky balancing this timing with the AF/ I start with 16 mechanical all in by 2k and 8 degs Vac I use the initial , just to get it started. This way you have aprox 26/28 degs in cruise, and 18/20 at WOT. Which will prevent detination on tje crapy gas we have. Haveing an adjustable Mach advance also helps. This might sound like allot of work, but the 5 plusK invested in the engine is worth it.
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