Poor Gas Mileage

[Bruce VA]

Need some advice on improving the gas mileage on my A Model (1929 Tudor w/ a Zenith B carb on a 31 engine) First, my odometer has been checked; it works fine. I have no fuel leaks. The car starts & runs fine. I start it cold w/ full choke, GAV 1 turn out, spark fully retarded. As soon as it starts, GAV to ¼ turn out, spark to ¾’s down. I rarely move the spark advance from ¾’s as I rarely exceed 45 mph. Timing is dead on. The timing pin fits easily in the slot in the gear; trailing edge of the rotor is just opposite the #1 tit in the distributor as points just start to open as observed w/ a meter. (I gained about 2 mpg after adjusting this) Timing confirmed w/ a light & marks on the crank pulley. Points set at .018 & confirmed w/ a dwell meter at 31*. Advance works as it should by observing the timing light. Plugs are a light brown. Not that it needed it, but carb was soaked in cleaner, blown out & rebuilt w/ all new flow tested jets, nylon jet gaskets, etc. Carb idle was checked w/ a vacuum gauge. Float level checked w/ a plastic tube; 5/8” from the carb seam. What can I do to improve the current 12 m.p.g. gas mileage? Thank you.

[Kahuna]

Bruce
It sounds like you have taken care of everything.
Here's all I can add:
Was TDC checked? If so, great. Otherwise, I would say to find someone with an Air/Fuel Meter and check things that way. Your engine may still be running rich.
As I think you are on the East coast, I don't know what your fuel is?
Where I live we don't have Ethanol and plugs are very whitish with proper A/F mix.
BTW, is your driving just around town, as in local driving? Or, highway? Makes a big difference.

[Bruce VA]

Tnx! Only TDC check was w/ the timing pin. Yea, in VA w/ 10% ethanol. Most driving is 40-45 mph on country roads, not much stop & go. This really bugs me because the last A Model I had in the 80's got close to 20 mpg w/ no effort on my part. Will check around for an Air/Fuel meter. Meanwhile, I'll try to lean it out a bit w/ the GAV. Run at 1/2 or 3/4 turn out instead of 1/4?

[TerryH]

I get over 20 mpg in my Town Sedan when cruising on the hiway, but much less when I am driving around town, with lots of stop and go. What are you getting on the hiway?

[Bruce VA]

Maybe 14 on just the highway. I'll see what you guys here have to say this evening & make whatever adjustments, etc, I can & then try again tomorrow w/ an 80 mile run on the highway. 40 miles each way. I'll gas up when I leave & then when I get back.

[J Franklin]

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Lean it with the gav all the way shut and see what happens. also play with the spark lever and run where you have most power without any pings or knocks. What plugs are you using?

[SDJason]

Originally Posted by J Franklin

Lean it with the gav all the way shut and see what happens. ...

If you do this, be sure to keep an eye on your temperature - things may run hotter, or possibly overheat depending on how lean you're running

[Bruce VA]

I'm using Motorcraft TT10 plugs. Re the GAV setting.....maybe I've got it backwards in my mind. I thought turning it in cut the air, thereby getting you a richer mixture. Wrong? Yea, I'm aware that a lean mixture can cause it to run hotter. I've got a 160* t-stat in it & rarely does it get much over that on the gauge.

[Bruce VA]

OK, got my head straight re the GAV. It sets in the bottom of the carb & actually controls the gas flow. Screw it in, it reduces the gas, ie, leans the mixture. But screwing the idle jet in cuts the air, thereby getting a richer mixture. Been 30 years since I had an A Model!

[springerpete]

Are your brakes dragging ? Tires correctly inflated ? Any air leaks around the intake or carb ? Is the throttle plate loose ? These are all things I checked to improve my gas mileage but I never got up to 20 mpg. Satisfied at around 15-16.

[mhsprecher]

I took a fairly long trip with mine recently and got 15 mpg. It was running great, but it still may be a little rich. I'd love to see it go higher.

[TerryH]

A properly running Model A should get somewhere around 20 mpg when cruising at 45 mph, and it is not real windy or hilly. If you are only getting 14-16, sounds like something is not right. I have been on 2 long trips in my Town Sedan, and it has a Snyder 5.5 head, and the Mitchell OD, but I also cruise at 55-60, and I still got about 22 mpg, going from S. Calif up to Yosemite, and then back. But in town, it is probably more like 14 mpg.

[DJ S]

Originally Posted by TerryH

A properly running Model A should get somewhere around 20 mpg when cruising at 45 mph, and it is not real windy or hilly. If you are only getting 14-16, sounds like something is not right. I have been on 2 long trips in my Town Sedan, and it has a Snyder 5.5 head, and the Mitchell OD, but I also cruise at 55-60, and I still got about 22 mpg, going from S. Calif up to Yosemite, and then back. But in town, it is probably more like 14 mpg.

The Mitchell OD does increase MPG. I usually get around 14-15.

[Bruce VA]

Brakes are adjusted properly & tires are inflated correctly; checked those things first. I put in a throttle bushing & a new throttle shaft, so that should be ok too. But, what Terry H is saying about 22 mpg on the highway & 14 around town might be the answer. Maybe I'm expecting too much. I'll see what tomorrow brings at 45/50 mph for 80 miles.

[Richard in Anaheim CA]

I generally get about 16.5 mpg on long trips with either a stock Zenith or a 32/36 Weber Carb. I have never got the 20 mpg many claim.

If I were particularly concerned with mileage, I would have my jets calibrated to accepted flow rates.

Yes, turning the GAV clockwise makes the mix leaner and gives better mileage. Some will run with the GAV closed and some won't. That is on the open road. In town you will have to open it 1/4 turn to prevent stalling at each stop sign.

[Mike V. Florida]

I don't know you so please don't take this personally. The problem may in part be the driver. What speeds (RPM) do you shift gears. How hard do you apply the gas to accelerate. How about stopping, foot off the gas in advance of the stop sign or light or wait until nearly the last moment? Is the 3/4 spark setting done because that's the way it's always been done or is that the setting that gives the max RPM's and no more movement after that?

As for mechanical, how's the compression?

[James Rogers]

Originally Posted by Bruce VA

I'm using Motorcraft TT10 plugs. Re the GAV setting.....maybe I've got it backwards in my mind. I thought turning it in cut the air, thereby getting you a richer mixture. Wrong? Yea, I'm aware that a lean mixture can cause it to run hotter. I've got a 160* t-stat in it & rarely does it get much over that on the gauge.

Get rid of these and get a set of Champion W18 plugs. They are a bit hotter and will burn all that gas instead of pushing it out of the exhaust.

[James Rogers]

Originally Posted by Bruce VA

OK, got my head straight re the GAV. It sets in the bottom of the carb & actually controls the gas flow. Screw it in, it reduces the gas, ie, leans the mixture. But screwing the idle jet in cuts the air, thereby getting a richer mixture. Been 30 years since I had an A Model!

This is correct but the GAV only affects the first 1/4 throttle. After that the main jet takes over.

[H. L. Chauvin]

Hi Bruce,

Sounds like after tinkering for days & trying everything you can think of, you are maxed out on trying different settings.

Thinking out of the box, I'm presently trying to figure out how can one make a Model A obtain 12 mpg after everything checks out as if the car was new.

The only 2 mpg gain you reported was observed when the trailing edge of the rotor was adjusted; however, maybe try re-checking timing like this below, plus checking these other two (2) areas:

I. Timing:

1. With spark fully retarded, rotate engine very, very slowly until timing pin slips in & hits bottom of timing pin hole. Do this several times until you master "feeling" bottom in the timing gear.

2. Next, when timing pin "bottom" is achieved, check to see if your points are just about to open.

a. This does not mean that your points are already opened just very, very little.

b. This does not mean you have to rotate the crank another 1/8" more to make the points almost open; but means they are closed, on the verge of opening, & with very slight crank movement, the points open, which can be verified with a test lamp if you have doubts.

3. To assure for compensating for slop in the rotor/distributor shaft, after this first step is successfully achieved, go to step (2) of (I) & rotate the engine 360 degrees & try again to "verify" that when timing pin hits bottom, points are just about to open.

II. Carburetor:

If this does not increase gas mileage, maybe try another "known" good carburetor, even though yours was rebuilt by Albert Einstein and/or Houdini; please remember both of these guys were very human, which means even though both were perfectionists, something minor could have been overlooked.

III. Vacuum Check:

If you have a vacuum wiper, an engine test with a vacuum gauge connected to the intake manifold cannot hurt either; very similar to a mpg tester; with a warm engine, at fast idle, one should obtain a steady needle reading between 19 & 20. With any other readings, or a jumping needle, report back what you have found.

Just hope this helps.

[sidevalve8ba]

Bruce,

You mentioned ethanol spiked gasoline early on. I do not know what part of Virginia you call home but there are close to 300 gas stations in this state that sell non-ethanol gas. Click on this link and see if any are near you. I have seen a 10% improvement in fuel economy in my own vehicles by using non-ethanol.

http://pure-gas.org/index.jsp?stateprov=VA

I hope this is of some help.