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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
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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
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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
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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 itís pretty much spot-on. I also just checked my spark plugs, and there is some black sticky-ish residue around the edges ó 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 Iím sure would give me better mileage ó but also feels very underpowered, so then Iíd wonder if that indicates a different problem? Doesnít seem like anythingís dragging, at least not severely, as it rolls downhill pretty freely.

Where I drive (near Salem OR), itís not mountainous or high altitude but it is somewhat hilly. Iíd 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? Iím guessing the former, but this is something Iíve 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

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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
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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 Iím confused as to why closing it all the way doesnít 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:
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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 donít have an air filter. Iíve 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 thatís because the fuel in the bowl warms up and expands when itís not circulating, does this indicate the float level is set too high? Iíve never adjusted the float level in this carb, so it could be that it needs to be adjusted; although, correct me if Iím 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 doesnít show signs of being too rich as the plug electrodes arenít sooty; and if itís 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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Old 04-25-2021, 04:00 AM   #21
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Default Re: 10mpg

I get around 20 MPG plus or minus that is imperial gallons so US gallons I suppose around 17 MPG . My ccpu likes to cruise at 45 MPH and I get up to high gear when I can . I do have a 28 phaeton with the AF 3" bore engine 28 BHP at 2600 RPM .the rear axle is 4.55 to 1 and it gets the same gas mileage but not the performance . 10 MPG seems too high to me if you can borrow another carb from someone who gets better mileage give that a try something is wrong somewhere . IMHO .

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Old 04-25-2021, 06:24 AM   #22
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Default Re: 10mpg

The 1971 Ford GTHO Phase 3 got 8 miles to the gallon at 100 mph:
"The fuel bill will also cause a few headaches - hard-pushed, the car does a neat 8 mpg. With slightly quieter driving it- will give 10.4 mpg - don't expect much more. As a fine, ultra-high performance car that will be beaten by nothing under $20,000"
https://www.whichcar.com.au/features...phase-3-review

So 10 mpg seems a bit thirsty.
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Old 04-25-2021, 06:38 AM   #23
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Default Re: 10mpg

Quote:
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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?
That definitely doesn't sound good. I don't need full throttle to go 40 mph up a moderate hill. My car is all stock. I run non ethanol 93 octane fuel.

Is your fuel fresh? Tire pressure correct?
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Old 04-25-2021, 07:59 AM   #24
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If the GAV is making a big difference, it could be that the main jet is clogged or the wrong size. Try a different carburetor.
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Old 04-25-2021, 08:01 AM   #25
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Default Re: 10mpg

Check this out. Although the presentation discusses why car won't go fast, the performance points also affect gas mileage.
https://onedrive.live.com/view.aspx?...Dzy090uDdd9_qQ
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Old 04-25-2021, 08:10 AM   #26
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Remember, model A gas mileage and speed stories are similar to fish stories, Trust but Verify. However 10 mpg seems somewhat low. Don't pay attention to where others have their GAV, it varies greatly per car, especially since you have a different carb. Set the GAV for smooth running and best power. Run the car around 45 mph for a tank, in reasonably level terrain and then check the mileage. Don't set the GAV any leaner than what runs the best. Advance the spark until it just starts to ping on acceleration, then back off a click or so. If you havent tuned your ear to what ping sounds like you can go to youtube and hear it in videos. Some people with enough hearing loss can't detect it. Take a young person with who can hear well, teach them what to listen to. If it still doesn't give you the mileage you're looking for then swap out the carb with one from a tested car. Let us know how it goes.
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Old 04-25-2021, 08:32 AM   #27
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Old 04-25-2021, 09:12 AM   #28
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Default Re: 10mpg

Be careful that you are not going too lean and losing power and thus gas mileage because you are on the lean side of the power curve. Your spark plug pictures suggest a good fuel mixture with a little oil usage so this probably is not the case. However, try less than full spark advance (3/4 of travel) and a little more than 1/4 turn (3/8) on the GAV to see if your engine wants just a little more to give the power necessary. I once tuned in a Harley carb that was giving poor gas mileage and power until I went richer and suddenly hit the sweet spot that gave both power and gas mileage.
BTW, at 55 mph you are entering the speed where air resistance is the overpowering driver for poor gas mileage. The Model A is as aerodynamic as a brick. Try some 40-45 mph mileage tests to see if there is a step improvement in your gas mileage.
I have been consistently disappointed with my mileage as well at 15-16 mpg but I drive a section of highway at 60+ mph going to and from work.
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Old 04-28-2021, 01:23 AM   #29
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Quote:
Originally Posted by Bob Bidonde View Post
Check this out. Although the presentation discusses why car won't go fast, the performance points also affect gas mileage.
https://onedrive.live.com/view.aspx?...Dzy090uDdd9_qQ
This is a very helpful slide deck, thanks for sharing it! I learned a lot from this.
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Old 04-28-2021, 01:44 AM   #30
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Alright, so you guys really got me thinking... Eagle, you suggested to advance the spark until my engine starts to ping, then back off a little. Starts to ping? I’ve never heard my engine do that when advancing the timing, and I always drive at full spark advance because it feels way underpowered otherwise! So, when you said that, I thought maybe my distributor cam is too retarded, since I can’t advance it far enough to get engine pinging. (Big Hammer also mentioned earlier that 90rpm at idle sounds like spark is too late). So I advanced the cam by 15-20 degrees, and wow — now I’m getting 15-17mpg instead of 10mpg, and I barely have to press the gas pedal to get to 40mph. What a huge difference! I still don’t think I hear a ping when I run at full spark advance, but now at least it feels like I stop gaining extra power when I go to a click or two before full advance, which means I’m probably hitting the top of the timing curve. I think I can probably get a few extra mpg’s by finding the right GAV setting now that the timing’s more optimal, fixing the exhaust leak between the exhaust pipe and the manifold, and staying between 35-45mph.

I’m not sure why I had to advance the cam 20 degrees to be able to get the optimal timing... spark plug gap too wide maybe? In any case, I’m happy that it works and don’t want to look the gift horse in the mouth. Thanks everyone for all your help on this!
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Old 04-28-2021, 06:42 AM   #31
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Default Re: 10mpg

Sounds like you got her fixed. I would, however, learn what ping sounds like. Ping is destructive and you just dont want to go there.
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Old 04-28-2021, 07:24 AM   #32
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Sounds like you got her fixed. I would, however, learn what ping sounds like. Ping is destructive and you just dont want to go there.
Good work on your part. Another happy member because of people like you ! Wayne
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Old 04-28-2021, 09:53 AM   #33
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Good news Eamon. Thanks for the feedback. You may not hear the ping if you have any hearing losses at higher frequency. But if you are at the top of the ignition curve, as you say, then you have the right timing. I call it the knee.
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Step on the gas, for tomorrow I die.
Forget the brakes, they really don't work.
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My car grows red hair, and flies through the air.
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