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Old 04-24-2021, 01:11 AM   #1
eamonford
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Default 10mpg

Hi all! I have a 1928 Tudor, and I get 10mpg. From reading other posts and articles around the internet, I’m getting the impression that this isn’t completely out of the range of what I should be expecting after 93 years, but still seems definitely on the lower end — I see some people are saying they get up to 26mpg. Does my gas mileage indicate a problem somewhere? I typically drive on back country roads at my engine’s top speed of 55mph, with full spark advance and the GAV at 1/2 turn (any less than that and I start losing some power). I’ve also replaced the original Zenith carb with a Schebler. A compression test shows each cylinder at about 64psi, which matches the Bratton’s spec. I’ve set the timing to be ~0 degrees when the spark advance lever is fully retarded. I have a thermostat installed, so temp gauge always shows coolant temp between 145-160 degrees. Other than a minor exhaust leak between the manifold and the exhaust pipe, my engine feels very healthy — I can even idle at about 90 rpm. Could it be that I need new valve seats? A ring job? Grateful for any suggestions. Thanks!
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Old 04-24-2021, 04:27 AM   #2
GerryAllen
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Default Re: 10mpg

I get 14 miles to gallon, very similar situation to you. Thermostat, Gav setting, water temp, the only thing is my average speed is 40-45 MPH.
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Old 04-24-2021, 05:20 AM   #3
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Default Re: 10mpg

Normal, flat city driving, you should get between 16 -20mpg. Make sure you don't have a gas leak. GAV should not be that far open. That's probably your problem. Check for intake air leak.
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Old 04-24-2021, 05:58 AM   #4
Keith True
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Default Re: 10mpg

You may have a speedometer problem,not a fuel mileage problem.
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Old 04-24-2021, 06:06 AM   #5
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Default Re: 10mpg

''From reading other posts and articles around the internet''

This statement has caused more problems than can be measured. It has resulted in billions of lost dollars and a millennium of lost time.My happiness increased ten fold the day I began disregarding anything I read at the temple of the screaming electron.

Sounds like your A runs nice and you probably enjoy every moment you spend driving and maintaining it.. enjoy!!
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Old 04-24-2021, 06:48 AM   #6
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I have topped 30 mpg but that's an imperial gallon. Even using the smaller US gallon, at 10 mpg, it is too thirsty and with that much fuel going through it, the cylinders will be lacking lubrication. Does it blow black smoke?
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Old 04-24-2021, 07:09 AM   #7
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Default Re: 10mpg

10 mpg ? I would consider 15 mpg on the low end. What rear end gears do you have? Are you checking tire pressure at 35 psi? Does your speedometer match a gps app in a smart phone? What do the spark plugs look like? 90 rpms idle sounds like late timing. My tail pipe burns a light gray color. Salem Or are you driving I'm mountains, a HC head would be helpful with power and fuel mileage !
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Old 04-24-2021, 08:03 AM   #8
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Default Re: 10mpg

Full spark advance might be a bit much.
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Old 04-24-2021, 10:35 AM   #9
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Default Re: 10mpg

I got 23 average over several thousand miles of driving to 50-65, full advance, closed gav with regular gas, haven't kept detailed records lately, with nj ethonal gas I still get over 100 miles on 5 gallons, but need 1/4 turn on gav to not be too lean, still use full advance most all the time, with closed gav I burn the plugs white , I have done testing with 4 gas analyzer under load to verify mixture and gav setting --- I could pass emission test as 2005 Honda
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Old 04-24-2021, 11:52 AM   #10
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Default Re: 10mpg

The motor sounds healthy, time to look elsewhere.
Take the car out for a drive 30 minutes or so and get an infrared temp gun.
Start looking at brakes, hubs, transmission, rearend.
If something is dragging your mileage down it will show pretty warm.

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Old 04-24-2021, 12:25 PM   #11
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Default Re: 10mpg

10 MPG is fine...enjoy the drive. I also agree the speedometer could be off slightly so it appears to be ten when its slightly more. I get ten MPG and drove roundtrip 450 miles to Gettysburg in 2017. Figured 100 miles max per tank....took me fine from gas station to gas stop.
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Old 04-24-2021, 01:02 PM   #12
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Default Re: 10mpg

Eamon, 10 mpg is too much. Look for parasitic drag as John Neilson advised. Look at the plugs to see if they are black, indicating too rich of a mixture. It also could be the way you drive and where you drive. If possible, try measuring mileage on a flat highway at a constant 50 mph. Ford advised the same for a mileage test. They had a setup where a small measured amount of fuel could be run through the engine and the mileage calculated by the distance traveled. The setup had valves where the fuel could be drawn from the tank or the measured amount.
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Old 04-24-2021, 01:19 PM   #13
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Default Re: 10mpg

Try driving at a slower speed the MODEL A likes speeds around 35-45 for best milage.
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Old 04-24-2021, 02:08 PM   #14
eamonford
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Default Re: 10mpg

Hey all, thanks a lot for the suggestions. I have checked the speedometer (and odometer) against a GPS, and it’s pretty much spot-on. I also just checked my spark plugs, and there is some black sticky-ish residue around the edges — photos attached. Does this indicate too rich a fuel mixture, or oil leaking into the cylinders? If it means too rich, then sounds like maybe I just need to drive with the GAV more closed, which I’m sure would give me better mileage — but also feels very underpowered, so then I’d wonder if that indicates a different problem? Doesn’t seem like anything’s dragging, at least not severely, as it rolls downhill pretty freely.

Where I drive (near Salem OR), it’s not mountainous or high altitude but it is somewhat hilly. I’d say the ground covered on my drives is about 50-50 flats vs rolling hills. I will try doing a flat highway test, as nkaminar suggested.

J Franklin: when you say the Model A likes 35-45mph for best mileage, would that mean driving pedal to the floor with GAV closed (or maybe 1/4 open), which would translate to about 40mph in my car, or driving with the GAV more open (like 1/2) and less foot on the gas? I’m guessing the former, but this is something I’ve always wondered about.

Thanks!



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Old 04-24-2021, 05:53 PM   #15
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Default Re: 10mpg

Those plugs say the motor is waaaay rich. Do you run an air filter? If so, try removing it and try again. After that, I'd start with the carburettor. Check float level first, then if that's OK, a set of flow tested jets.
I'm sure others will add to that.
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Old 04-24-2021, 06:03 PM   #16
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Default Re: 10mpg

I checked mine just the other day, and am getting about 16. That is in town, or climbing back and forth over a small pass.
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Old 04-24-2021, 06:22 PM   #17
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Default Re: 10mpg

I have a different opinion than Synchro. The black around the edges is carbon from oil and I would not worry too much about that. There no sooty black deposits on the electrodes which would indicate running rich. The plugs look like the fuel ratio is about right. If you close the GAV all the way and loose power then that is too lean. The sweet spot is where you want to run the carburetor. With alcohol in today's gasoline the Model A will want to run with the GAV a little more open than in 1930.
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Old 04-24-2021, 08:35 PM   #18
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Default Re: 10mpg

I get around 17 around town and 20-ish on out on the road on tours averaging 45 mph. I generally keep the GAV nearly closed other than when the car is cold. Most say 1/4 open is the norm. All cars seem to be a little different. I never run full advance. Generally 1/2 down the quadrant seems to work best.

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Old 04-24-2021, 08:44 PM   #19
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Default Re: 10mpg

Quote:
Originally Posted by nkaminar View Post
I have a different opinion than Synchro. The black around the edges is carbon from oil and I would not worry too much about that. There no sooty black deposits on the electrodes which would indicate running rich. The plugs look like the fuel ratio is about right. If you close the GAV all the way and loose power then that is too lean. The sweet spot is where you want to run the carburetor. With alcohol in today's gasoline the Model A will want to run with the GAV a little more open than in 1930.
Agree. The plug aside from the black deposits on the threaded part, looks text book, the electrodes are tannish that is a good sign. That is where it counts. Black sooty deposits on the electrodes would indicate too rich of a mixture. I don't see that here.

Our '29 Tudor got 20 MPG all day long, this is Cornbelt country all flatlands no mountains
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Old 04-25-2021, 12:29 AM   #20
eamonford
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Default Re: 10mpg

So, I did a few test drives today with different GAV settings, and it turns out I still get about 10 mpg even with the GAV at 1/4 turn and all the way closed. I know the GAV is doing something, as it instantly affects the engine power when I change it, but I’m confused as to why closing it all the way doesn’t seem to improve the mpg at all. I should note that I was driving with the gas pedal all the way down in order to maintain 40mph. I did order an infrared temperature gun, so that I can check for drag as John Neilson suggested. Other than that though, why would my mpg be unaffected by closing the GAV all the way?

Quote:
Originally Posted by Synchro909 View Post
Those plugs say the motor is waaaay rich. Do you run an air filter? If so, try removing it and try again. After that, I'd start with the carburettor. Check float level first, then if that's OK, a set of flow tested jets.
I'm sure others will add to that.
Nope, I don’t have an air filter. I’ve also not observed any gas leaking when idling, although after I shut off the engine, gas does leak out of the intake on the carb for a few minutes. I assume that’s because the fuel in the bowl warms up and expands when it’s not circulating, does this indicate the float level is set too high? I’ve never adjusted the float level in this carb, so it could be that it needs to be adjusted; although, correct me if I’m wrong, my understanding is that if the float level is not set properly, the only way it could affect gas mileage is by making the mixture too rich or too lean? From what nkaminar and Jeff have said it seems like mine doesn’t show signs of being too rich as the plug electrodes aren’t sooty; and if it’s too lean (beyond what can be controlled by the GAV), then I would think the gas mileage would be higher.

By the way, just wanna say as someone with no experience prior to this Model A, I learn a lot from reading all your differing opinions It really helps me to think through the cause and effect of these scenarios.
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