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Why does engine run best with GAV almost closed My engine runs best with GAV nearly closed. It will start that way also. The carb is totally ok and has been rebuilt professionally.
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Re: Why does engine run best with GAV almost closed The GAV controls the amount of fuel that reaches the cap jet in addition to what it receives from the comp jet. The comp jet is much smaller that the cap jet. If the GAV is closed the only fuel reaching the cap jet is through the comp jet. When you open the GAV it ports fuel around the comp jet and the cap jet receives much more fuel.
For everything to work correctly each jet in the carburetor should be flow tested to be sure they are within the deign spec. Most reproduction jets are wide of the mark. My car runs best with the GAV open about a half a turn. More than that and it will run rich. As long as you can control how your car runs with the GAV it is probably ok. Your comp jet may be on the large size. Tom Endy |
Re: Why does engine run best with GAV almost closed I really recommend using flow-tested jets. I installed a set from Renners Corner and it made a noticeable difference in pep and smooth performance.
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Re: Why does engine run best with GAV almost closed One of mine runs best at about 1/4 open. The 30 runs best almost closed. I am no expert, but my understanding is to adjust to where it runs best.
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Re: Why does engine run best with GAV almost closed There's no one MAGIC setting for the GAV. Carbs VARY, WEATHER, ALTITUDE, HUMIDITY varies & on & on.
With a warm engine, run @ a steady 25 MPH in SECOND GEAR, adjust GAV for best running & LEAVE IT ALONE! AND, if your GAV affects your idle, YOU'RE IDLING TOO FAST. I CAN'T believe all the confusion with things like setting the dad blamed timing & where should I set the GAV? Some seem to WANT to COMPLICATE a SIMPLE car. Would a MIDOL help me? Bill W. |
Re: Why does engine run best with GAV almost closed Make sure your proff reblt carb has a proper set of flow tested jets and that your float level is set just right.. They make all the difference...
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Re: Why does engine run best with GAV almost closed If idle and comp. jets are correctly sized you should be able to close the GAV and the engine run OK.
Running with the GAV open will reduce your MPG during normal driving. I believe the Owners Manual tells you to close the GAV for normal driving. Ron |
Re: Why does engine run best with GAV almost closed I would be very careful about driving at cruising speed with the GAV closed. This causes the engine to be running lean and increases exhaust gas temperatures (EGT) that could do damage to the engine.
Several of us have constructed an engine running stand that is equipped with a number of sensors, including an EGT sensor. We noticed that when the GAV was closed the EGT would increase by quite a bit. The carburetor on the test stand has re-sized jets installed. It is also a good idea to open the GAV more and retard the spark slightly when climbing a long steep grade. Tom Endy |
Re: Why does engine run best with GAV almost closed You don't say which carb you have. If it happens to be a "B" carb they are designed to run with the GAV closed after warm-up.
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Re: Why does engine run best with GAV almost closed So, I gues the next question is, how do you know it's running right. I notice a difference from a full turn to only a quarter turn open but not much (if any) between a quarter turn open and fully closed.
Regards, |
Re: Why does engine run best with GAV almost closed I think your situation is a cause for pride, not concern. It means that you've got a nice tight intake system that is not leaking any air in that needs to be balanced by extra fuel enrichment (i.e., opening the GAV). The most common problem with old carbs is a worn throttle shaft: Jillions of vibrations jamming against the throttle linkage takes a toll, and provides a leakage path for more air to leak in, causing the car to run too lean. The problem is, this is a project--there's no easy fix, so in my experience many rebuilders just clean it up, clear the passages that can be reached, change the jets and gaskets, paint it up and hope for the best.
Steve |
Re: Why does engine run best with GAV almost closed What do you think it should be running at? And why?
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Re: Why does engine run best with GAV almost closed 1 Attachment(s)
Welcome to the site Go doc. Do you have the Model A owners manual?
This is from an owners manual (bolding is mine), The section on starting 3. If the engine is cold, turn the carburetor adjusting rod one full turn to the left to give it a richer mixture for starting. This rod serves both as a choke for starting and as an enriching adjustment. Next pull back the rod, at the same time pressing down on the starter button with your foot. The instant the engine starts, withdraw your foot from the starter button and release the choke rod, next advance the spark lever about half way down the quadrant. When the engine warms up, turn the adjusting rod back to the right. Never drive continuously with adjusting rod more than ¼ turn open. The section on carburetors Adjustment of Carburetor The method of regulating the carburetor for ordinary driving .conditions is to tum the carburetor adjusting rod to the right until the needle just seats, then turn the rod back approximately one-fourth of a turn. |
Re: Why does engine run best with GAV almost closed Minervas' Zenith was SUPERB, in ordinary temps, she would start with NO CHOKING, plugs burned a light TAN & ran fine with the GAV CLOSED!
I only used 1/4 turn of the GAV, or had to choke her, when the temps got down to 28 to 32 degrees. I did run a 160 thermostat, which really helped. Fortunately, I DON'T have a COLD garage. Bill W. |
Re: Why does engine run best with GAV almost closed Quote:
the next paragraph---"On long trips some drivers make a practice of driving with the adjusting rod turned all the way off" I have run my car under load with an emission machine hooked to the tailpipe, both with regular gas and ethonal gas, with regular gas my carb runs a little rich (4% CO gav off), with ethonal gas--gav off is too lean at 0.05% co, my jets are a good compromise for both fuels, , I checked the mixture up to 3200 rpm, baisically I wanted to know the best positions for my GAV, up to about 40 the car will run fine closed/1/4 turn, above 60 it wants almost 1/2 turn to have CO in the 2-4% range that the car runs good and gets good fuel mileage |
Re: Why does engine run best with GAV almost closed So in other words, Go doc, "Since it's not broke, don't try to fix it"! This is a better idea than "Fix it until it's broke"!
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Re: Why does engine run best with GAV almost closed Last summer I had been having backfiring problems a lot. It was nerve racking. I had the carb rebuilt and now I open the GAV 1/8 to 14 turn open. This has eliminated the backfiring. However if I close the GAV and drive my '30 for a distance, it will backfire when I turn the engine off.
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Re: Why does engine run best with GAV almost closed Quote:
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Re: Why does engine run best with GAV almost closed Quote:
Bill W. |
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