Fuel/air mixture setting

W

woodrow

Senior Member
Just changed plugs. I had been running way too rich and the old plugs were really fouled. Test drove the car a few miles and ran so much better with new/clean plugs. I turned the mixture control all the way (clockwise) lean to get the starting point to set the mixture about 1 1/2 to 1 3/4 turns rich based on suggested guidelines. When I got all the way toward lean I expected the engine to falter a bit but with it all the way clockwise I couldn't tell any difference in the way it ran. Do I need other adjustments or is that OK? This is a 1930 Model A roadster and the carburetor is a Zenith.
 
I think you might have a dirty carb there is a vent hole that sometimes gets clogged the hole goes from the cap jet and the gas get a gasket set and take it apart soak it good and blow out every orfice
 
in the owners instruction book it says that good drivers can get excellent gas mileage driving with gav all the way closed
 
The valve was all the way closed for the first 10,000 miles in my car till I put a down draft on it. Not all engines are created equal.
 
If you have a Zenith they the GAV should not need to be that far open. It should run fine at about 1/4-3/4 turns open. If not then there is something wrong with it that should be able to be fixed fairly easily. These are simple carburetors and a lot of us have quite a bit of knowledge about them.
Also, what spark plugs are you using ?
 
woodrow said:
Just changed plugs. I had been running way too rich and the old plugs were really fouled. Test drove the car a few miles and ran so much better with new/clean plugs. I turned the mixture control all the way (clockwise) lean to get the starting point to set the mixture about 1 1/2 to 1 3/4 turns rich based on suggested guidelines. When I got all the way toward lean I expected the engine to falter a bit but with it all the way clockwise I couldn't tell any difference in the way it ran. Do I need other adjustments or is that OK? This is a 1930 Model A roadster and the carburetor is a Zenith.
Click to expand...

Recently had the same problem. Took my Zenith apart, cleaned all the passages, checked the openings on the 4 jets, put it back together, test drove
the car. The GAV is set about 1/8 of turn open to start and warm up, can drive at that setting or completely closed.
 
(1) Last step in a tuneup is carburetor adjustment, so ignition refresh including timing comes first;
(2) Engine at operating temperature & GAV 1/4 turn open;
(3) Starting at 1.5 turns open, turn idle air screw in or out to get the highest idle speed;
(4) Adjust idle speed screw.
 
Thanks for all the good answers. Sure do appreciate your comments. First thing I'll do is re-set the mixture control to almost closed---runs great like that. Thanks again.
 
Overlooked answering the questions about what plugs I used: The ones I removed were Champion C-4. Checked replacing those with the same thing, however when I checked the price with one of the Model A suppliers they are $37.00 each. Went to a local NAPA dealer and bought Champion 561 plugs (that is the number on the box. Four of those were $33.00 total. Anyway, the new plugs run great. I'll keep the old C-4 and clean them up.
 
My Coupe runs perfectly okay with the GAV closed. This probably indicates a damaged GAV needle seat. Probably not the needle as I had replaced it. My plugs are cleanest with the GAV closed, so I run that way.
 
woodrow said:
Overlooked answering the questions about what plugs I used: The ones I removed were Champion C-4. Checked replacing those with the same thing, however when I checked the price with one of the Model A suppliers they are $37.00 each. Went to a local NAPA dealer and bought Champion 561 plugs (that is the number on the box. Four of those were $33.00 total. Anyway, the new plugs run great. I'll keep the old C-4 and clean them up.
Click to expand...

Champion 561 are W16Y's so you're good to go.
 
woodrow said:
Just changed plugs. I had been running way too rich and the old plugs were really fouled. Test drove the car a few miles and ran so much better with new/clean plugs. I turned the mixture control all the way (clockwise) lean to get the starting point to set the mixture about 1 1/2 to 1 3/4 turns rich based on suggested guidelines.
Click to expand...

That suggestion is not for the GAV, but for idle circuit fuel mixture adjustment. Which are you referring to, the knob on the right side of the dash, or the adjustment screw on top of the carb?
 
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