06-03-2021, 04:39 PM | #1 |
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GAV Question
So how far open do you run your GAV? Will a lean or rich setting cause a car to run hot?
Thanks Ron |
06-03-2021, 04:56 PM | #2 |
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Re: GAV Question
The GAV adjustment is affected by the size of the cap jet and the comp jet. When the GAV is closed fuel that is emitted by the cap jet is determined by the size of the comp jet. When you crack the GAV open you are porting fuel around the comp jet so that the cap jet will emit more fuel. If the comp jet has been drilled out to the same size as the cap jet the GAV does not have any control.
Each car is going to be different depending on the sizing of the two jets. If the two jets are within spec (most are not) the GAV adjustment should be between 1\4 and 1\2 a turn cracked open for normal driving. The jets in my Vic have been properly re-sized and I run with the GAV cracked open 1\2 turn for normal driving. When climbing a steep mountain grade I open the GAV more and back off on the spark advance a little. Tom Endy |
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06-03-2021, 06:30 PM | #3 |
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Re: GAV Question
Explained well Tom. FYI; I don't know anyone that drills their jets.
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06-04-2021, 12:12 AM | #4 |
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Re: GAV Question
I did testing on emission machine under load , on 'regular" gas I got 3-4% CO with GAV closed, ran fine, gas mileage over 20mpg
Then NJ got 10% ethonal, this made the car too lean with the GAV closed, 0,5% CO (car would pass emissions as a 90s car), good running took 1/4 open up to 60, 1/2 above 60. I found that 3-4 % the plugs would burn light tan, at 0,5%-2.0% they burn pure white When I used gasoline with over 25% diesel it would take 1-2 turns to even run |
06-04-2021, 07:21 AM | #5 |
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Re: GAV Question
Normally a richer mixture will make an engine run cooler because of the latent heat of evaporation of the gasoline (and ethanol). There are limits and this pertains to the normal range of air/fuel ratio.
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A is for apple, green as the sky. Step on the gas, for tomorrow I die. Forget the brakes, they really don't work. The clutch always sticks, and starts with a jerk. My car grows red hair, and flies through the air. Driving's a blast, a blast from the past. |
06-04-2021, 08:35 AM | #6 |
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Re: GAV Question
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Bob Bidonde |
06-04-2021, 11:35 AM | #7 |
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Re: GAV Question
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06-04-2021, 02:40 PM | #8 |
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Re: GAV Question
I am somewhat confused. My car starts @ 1/4 turn open, idles perfect. Will not
run past 10 MPH. Have to open gav to 1 1/2 turns, car runs up to 35 MPH, open gav to 2 1/2 turns, car runs perfect up to 55 MPH, runs cool (160 degrees). I can leave gav @ 2 1/2 turns will slowing down or even stop and start again. Turn ignition off. Turn ignition back on touch starter, instantly starts. When on line and found this:ZENITH CARBURETOR ADJUSTMENT Turn idle adjusting needle in lightly against its seat, then back out needle l 1/2 turns as a preliminary adjustment. With throttle held in closed position, turn throttle stop screw in until stop screw just contacts throttle stop and then turn stop screw in 1 1/2 additional turns as a preliminary idle speed setting Set main jet adjusting needle at 4 1/2 full turns open. Start engine and let it run a few minutes until warm enough for final adjustments. Set the throttle stop screw for the desired idling speed. Set the idle adjusting needle for smooth idling. Turning the needle in (clockwise) reduces air and makes the mixture richer, while turning it out (counter clockwise) admits more air into the mixture making it leaner (avoid using a mixture that is too lean). To set the main jet adjustment, hold the throttle open so that the engine is running at about 1/2 its normal operating speed. Turn the adjusting needle toward its seat until it causes the engine to give evidence of a lean mixture by running irregularly. Then turn the needle away from its seat, carefully counting the turns made until the engine shows a trace of rich mixture. Set the adjustment. Then at just about halfway between the lean point and the rich point, hold the adjustment at this point and tighten the packing nut so there is no leakage of fuel around the adjusting needle. Note: Check the fuel line connections so there is no leakage. Look at magneto points and make sure they are not pitted and are adjusted to the proper gap (.020" if Fairbanks Morse - .014" to .016" if Edison Splitdorf). Check spark plug to make sure it is clean and properly gapped at .027".
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06-04-2021, 02:47 PM | #9 | |
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Re: GAV Question
Quote:
Not sure what those adjustments are for, but, they aren't for our stuff. Especially the last paragraph. |
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06-04-2021, 02:52 PM | #10 | |
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Re: GAV Question
Quote:
what confused.
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06-04-2021, 02:55 PM | #11 |
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Re: GAV Question
It's for a tractor.
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06-04-2021, 02:59 PM | #12 |
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Re: GAV Question
WOW!! Wonder why my car won't run unless I use use those settings as I
described? I would appreciate very much if someone would have an idea as to how I can fix this. Thanks.
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IN GOD WE TRUST - SEMPER FIDELIS John Last edited by jayvee34; 06-04-2021 at 03:13 PM. |
06-04-2021, 03:24 PM | #13 | |
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Re: GAV Question
Quote:
I'm not sure what rpm the main jet kicks in at, but you might could test this hypothesis by throttling up above where the main jet kicks in and then closing the GAV. In theory the engine would continue running off the main jet, and then when you lowered the rpm, the main jet would shut off and the engine would die immediately. |
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06-04-2021, 03:32 PM | #14 |
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Re: GAV Question
You can see in this image, the cap jet is fed both from the blue pipe and the green pipe. Green pipe is the GAV, blue pipe is the comp jet. Sounds like you're getting nothing via the blue pipe, so there could be a problem with the comp jet or the secondary well.
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06-04-2021, 04:12 PM | #15 |
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Re: GAV Question
John, There is a really good site for all things Zenith. For your situation see: http://model-a.org/mixture_lean_heat.html. For a good explanation of the different parts see: http://model-a.org/components_full.html.
The Zenith carburetor seems simple but the devil is in the details.
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A is for apple, green as the sky. Step on the gas, for tomorrow I die. Forget the brakes, they really don't work. The clutch always sticks, and starts with a jerk. My car grows red hair, and flies through the air. Driving's a blast, a blast from the past. |
06-04-2021, 04:15 PM | #16 |
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Re: GAV Question
alexiskai, Thank you so very much. I will go to work on it. I hope you don't mind that
I copied the attached picture. Being a Zenith Carb dummy I will need to refer to it. Thanks again.
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06-04-2021, 04:19 PM | #17 | |
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Re: GAV Question
Quote:
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06-04-2021, 04:21 PM | #18 |
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Re: GAV Question
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