Poor gas mileage

W

woodrow

Senior Member
Recently I posted a question about our '30 coupe and the poor gas mileage. I showed a picture of the Zenith carb, which had an air filter. A suggestion was made that I remove the air filter, which I did, however seems like I'm still getting less than 7 or 8 MPG. Then I realized I was running with the choke rod all the way in, turned clockwise and started running with it about 1 1/2 turn counter clockwise, but the mileage is still very low---about the same as before. Should I turn the choke rod more to counter clockwise or have the carb rebuilt? I'm open to suggestions. The car really runs great and I don't smell gasoline but sure would like to get the mileage to a more reasonable level. Thanks
 
Turning the choke/mixture rod counterclockwise will richen the mixture and reduce the mileage more. Turn the mixture rod in until it seats. Then turn out 1/4 turn for running.
 
How long are the trips and how many stops along the way?
Stop lights and stop signs are mileage killers.
How do you check fuel economy?
 
7 or 8 miles to the gallon is not normal even with some stop and go driving.
Pull a spark plug and check to see if it's color is black and looks sooty.
If so recalibrate your carb.

Fredski
 
All of the above advice is good, especially timing.

You should also check the compression of each cylinder with a compression tester gauge. I've owned some A's with low compression (due to worn rings or bad valves -- or both) that got poor gas mileage. No amount of fiddling with the carburetor would fix it. You may just have a tired engine.
 
Have the four jets in your Zenith been flow tested? If not, that could be your problem. Over the years people have been poking welding tip cleaners through the originals to clean them, and most of the reproductions are not much better. Most are way too big allowing too much fuel to flow. If you have a proper set of jets that are within the flow window, you should set your GAV at somewhere between a quarter and three quarters open.

Tom Endy
 
29spcoupe said:
Turning the choke/mixture rod counterclockwise will richen the mixture and reduce the mileage more. Turn the mixture rod in until it seats. Then turn out 1/4 turn for running.
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Well hell...now I know why my gas mileage is crap....I've been turning the GAV in the wrong direction!!!!!!!!:mad:
 
That is half the mileage you should be getting.
At this rate, you should have black smoke pouring out the pipe in a huge cloud, and your plugs should look like blobs of fluffy charcoal.
Something else is wrong besides carb/mixture.
I hafta guess there is a leak somewhere

Also, please describe exactly what math you are using to determine mileage.

Start by pulling a plug, get a pic, and post it. We can go from there
 
Few month ago, my car got exactly the same gas mileage but smells gas. I cleaned carb and filter, changed the float value shim and now : #14mpg !
 
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Tune your car with the GAV 1/8 to 1/4 turn open. Also take advantage of modern gasoline by setting the timing more advanced than at TDC where the mark in the camshaft gear will put it. Run with the GAV no more than 1/4 turn open, and the spark lever all the way down.
 
Bob Bidonde said:
Tune your car with the GAV 1/8 to 1/4 turn open. Also take advantage of modern gasoline by setting the timing more advanced than at TDC where the mark in the camshaft gear will put it. Run with the GAV no more than 1/4 turn open, and the spark lever all the way down.
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I would never do either. 28* advance is the most I'd use for the stock head, and even less for the higher compression head, like about 23*. I want my babbit to last.:)
 
Tom Wesenberg said:
I would never do either. 28* advance is the most I'd use for the stock head, and even less for the higher compression head, like about 23*. I want my babbit to last.:)
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You beat me to it. and don't forget about the Pistons and general overall engine health
 
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I’m haveing the same problem. About 8 miles per gallon. Going to check the gva
Think I know witch screw that is. But what does GAV stand for????
Woodrow, Did you fix your problem?
 
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Bob C said:
GAV=Gas Adjusting Valve You turn the choke rod to make adjustments.
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Though that was the fuel mixture in the cab. Lean/rich
Been playing with that one. Turn it too far closed and then I lose power. Got it adjusted about 3/4 turn out. Runs tops.
 
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