Can you run a Model A too lean?

[29 Tudor]

My A runs good with the GAV about 1/4 turn open after warming up. Just pulled to plugs for a routine check and they are all WHITE! Last time I looked at them, I had been running with the GAV at about 1/2 turn out and the plugs were a very nice light tan. I leaned it down a bit to see how it responded and while I don't think it has QUITE the power it did at 1/2 turn, it runs well. I have a feeling I'm running it a bit too lean.

Any thoughts or comments?

Thanks,

Steve

[Jim Brierley]

they can definitely be run lean. while some of the color of your plugs may be due to modern gas it would be better to richen it a bit instead of being sorry later. i think if you do a careful mileage test/comparison you would find little if any savings by running it lean.

[ford3]

with no lead in the new gas the plugs will be white, but it would be best to richen the mixture just a little, if it ran good at 1/2 turn open and the plugs weren't fould I would go back to that setting, to lean can led to a burnt piston

[29 Tudor]

Good thoughts, thanks. It's a lot cheaper to buy a little more gas than tear it down for valve/piston work.

Thanks guys!

Steve

[tbirdtbird]

the more pressing problem is burning the valves.
White is too hot.
They should be tan

You can't seriously be concerned about gas mileage now can you. That is a concern only in the realm of modern boring cars. This is your fun car, who cares about mileage??
Unless tearing the motor down for a valve job is someone's idea of fun....

oops guess you already figured that out! Composing at the same time....

[Tom Bellfoy]

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One person may say his GAV is set at 1/4 turn open when running, another may say 3/4 turn. I normally run mine almost 1/4 open and when I sense the motor missing or starving for gas I open the GAV accordingly to run smooth. Correct me if I'm wrong but I think the GAV position is very dependant on the diameter of the orifice on the compensator jet

[Patrick L.]

So how much did the fuel mileage change once going to 1/4 turn ?

[huddy]

Just an FYI, for interest only:

Extensive research on aircraft engines has proven that for a normally-aspirated, fuel injected engine, running lean of peak does absolutely no damage to the engine, and results in running at peak power and efficiency. This is done with EGT measurements on each cylinder, not practical for most auto engines that don't have separate cylinder heads. The technique is to lean the hottest cylinder for 50 deg C lean of peak temperature. This works best when the engine has been equipped with balanced injectors. I would think for a water-jacketed engine it is less of a problem as temperatures would tend to be more evenly balanced. The technique does not translate well to carbureted engines, and is not recommended for turbocharged engines.

What the developers found is that a normally aspirated engine will quit from fuel starvation before it can get hot enough to cause damage.

See this article: http://www.gami.com/articles/frugalflyer.php (NOTE the article has a video that automatically opens, so you might want to mute your sound).

Be aware that there is still some controversy about this, between old timers and modern flyers, but I am unaware of any actual documented engine damage as a result of operating this way. For autos, YMMV.

[mshmodela]

So is this a job for MMO!

What say you Model A, experts!

As for me, I can say is after running with 4oz of MMO/10gal of gasoline for 3-4 weeks my engine sounds a bit different --I'd say smoother...

[Patrick L.]

Originally Posted by huddy

Just an FYI, for interest only:

Extensive research on aircraft engines has proven that for a normally-aspirated, fuel injected engine, running lean of peak does absolutely no damage to the engine, and results in running at peak power and efficiency. This is done with EGT measurements on each cylinder, not practical for most auto engines that don't have separate cylinder heads. The technique is to lean the hottest cylinder for 50 deg C lean of peak temperature. This works best when the engine has been equipped with balanced injectors. I would think for a water-jacketed engine it is less of a problem as temperatures would tend to be more evenly balanced. The technique does not translate well to carbureted engines, and is not recommended for turbocharged engines.

What the developers found is that a normally aspirated engine will quit from fuel starvation before it can get hot enough to cause damage.

See this article: http://www.gami.com/articles/frugalflyer.php (NOTE the article has a video that automatically opens, so you might want to mute your sound).

Be aware that there is still some controversy about this, between old timers and modern flyers, but I am unaware of any actual documented engine damage as a result of operating this way. For autos, YMMV.

As mentioned, this is only good for injected engines with proper injectors and monitoring. Good individual cylinder exhaust temp monitoring has only fairly recently been made available.
And, yes, there is still controversy about this among pilots. Habits are hard to change.
Planes with nothing more than a carburetor [ or factory injectors] and tach [ or single exhaust temp probe/gauge] are still leaned the old fashioned way, just rich of peak.

[huddy]

I was going to do it in a Bellanca Viking 300 but ended up selling it before I could install balanced injectors. (Actually you get an adequate balance yourself with a coke bottle, stopwatch, and set of fine drills). But I think regardless of fuel system, running a non-turbo engine very lean will stall it more often than it will damage it. Problem with carburetors is that there's really no way to assure uniform fuel mixture in each cylinder.

I don't pretend to know how this applies to old Fords, even tri-motors, so I'll just shut up at this point… ;-)

[mot]

a friend of mine who ran his lean passed me
we were on the freeway (Idaho,no traffic)
and as he went by i could see through the hood louvers and his manifold was red hot and glowing

[tbirdtbird]

maybe he was cooking his dinner on the manifold....

[James Rogers]

Correct me if I am wrong but, the GAV only affects the first 1/4 of the throttle. The rest of the throttle is adjusted at the air mix screw so, 1/4 or 3/4 only affects your engine at idle and slightly above.

[Hicktick]

When I drag raced I had a high speed lean out button that cut the fuel in the last 300 feet of a close race .

As long as you have plenty of pistons you can win . The lean out really brings the power of the engine to the max for a very short time .


,,,,

[Patrick L.]

Originally Posted by huddy

I was going to do it in a Bellanca Viking 300 but ended up selling it before I could install balanced injectors. (Actually you get an adequate balance yourself with a coke bottle, stopwatch, and set of fine drills). But I think regardless of fuel system, running a non-turbo engine very lean will stall it more often than it will damage it. Problem with carburetors is that there's really no way to assure uniform fuel mixture in each cylinder.

I don't pretend to know how this applies to old Fords, even tri-motors, so I'll just shut up at this point… ;-)

I think so too. The max exhaust temp is at optimal fuel mix and thats where I believe the damage happens. Either leaning to rich of peak or lean of peak is about cooling the combustion temps and therefore the exhaust temp. Actually the cooling occurs quicker when lean of peak. Less fuel is burned during lean of peak operation and at todays 100LL prices it means quite a savings. I think I remember reading an article about Charles Linberg using/teaching this technique during WW2.

[MikeK]

Don't confuse plug color with indication of fuel mixture. If your warmed-up engine has it's running sweet spot at some GAV setting, but the plugs are white at that setting the problem is likely too high a heat range plug. The plug color indicates running temperature of the plug tip itself, affected primarily by the heat range design, not directly by the fuel mix ratio.

A stoichiometric running ratio of 15:1 is too lean and will damage valves, yet a way-cold plug in that engine will be gray and misleading. A stoic mix of 12:1 is too rich for cruising but a way-too-hot plug in that engine will be light colored and misleading.

Try a lower heat range plug. To properly measure mixture you need some type of exhaust gas content analysis, like an oxygen sensor. Plug color does not directly relate.