GAV Setting
 

If the GAV is turned do to the closed position will/should the engine stop? I have a carb. that doesn't. If this is a problem how can I repair it to get it to shut completely?

Thanks for any help.

Re: GAV Setting
 

No I run mine about 1/4 open,all vary!

Re: GAV Setting
 

I do the same while driving.
What would I like to know is if I turn the GAV all the way in should the engine quit?
I have read that that is part of the checks when doing a carb rebuild.

Re: GAV Setting
 

It will start to run rough,turn till u find the sweet spot,

Re: GAV Setting
 

It should not quit running tho

Re: GAV Setting
 

The GAV setting is dependent on the sizing of the comp jet and the cap jet. The setting of the GAV will be different from car to car. If the two jets are flowing within specifications the setting of the GAV should be a nominal 1\4 to 3\4 open. The comp jet has a small flow and a narrow window. It ports fuel into the secondary well where the cap jets draws its fuel. The cap jet has a much larger flow rate. The GAV valve is a means to port fuel around the comp jet into the secondary well. If the comp jet has been drilled out to the same size as the cap jet, the GAV then has no affect no matter where it is set.


Tom Endy

Re: GAV Setting
 

I was told that the Zenith was setup at factory to run at Detroit (essentially sea level) with 1/4 turn as owners manual says.

Note: Model B is another animal the GAV needs to be closed after warm up.

Then if a certain carb was a little rich or if you drive it at higher altitude you could lean it out with the GAV if needed.

The additional fuel provided by opening GAV as Tom Endy said is needed to keep engine running after a cold start until engine warms up. Then return to 1/4 when warm.

If extra GAV is needed on cold start the engine will start, run a second two and die ... opening GAV to about 1 turn (some a little more if really cold) will allow it to run while cold before it warms up.

Also opening the GAV up a little more when pulling a long hill or slogging through sand or mud for extended time gives extra power needed. I think the operators manual talks about this.

Re: GAV Setting
 

Re: GAV Setting
 

Remember, when closing do not turn tight. Just to the point it stops.

Ours will still run with GAV closed. Not well, but still running.

Starts when cold at full turn, than I close to about quarter turn. We live on Long Island Sound (sea level). Enjoy.

Re: GAV Setting
 

Re: GAV Setting
 

My car doesn't quit with the GAV closed, it just runs rough. I just turn almost 3/4 to start when cold and then run about 1/3 to 1/2 turn when warmed up. I have never heard that the engine has to quit when turned all the way closed.

Re: GAV Setting
 

The early Zenith carburetors had a screw-in brass GAV valve seat in the base of the GAV tunnel. Ford eventually did away with them because many people would close the valve tight. The needle valve is also brass. Brass on brass has a tendency to seize. The result was the needle seized in the brass seat, and when the driver tried to open the GAV it unscrewed the valve seat.


The brass valve seat looks very much like the comp jet. Often people have installed the valve seat where the comp jet is supposed to be. The result is GAV control is negated.


If you leave the brass GAV valve seat out of an early carburetor, the GAV control is also negated.


Tom Endy

Re: GAV Setting
 

Your engine should not quit, at least from my experience mine doesn't

The GAV is an interesting manual adjustment for added fuel under some circumstances. Ford Carbs generally run the engine lean. That is part of the design. The GAV is there to adjust fuel flow at driving speeds, primarily, and also for Altitude and weather conditions. For me the hard part is getting the engine to idle slow enough to keep running and then messing with the GAV and readjusting them both again until I reach somewhere around 3/4 turn open on the GAV and at slow idle. I have adjusted the GAV at running speeds also and that seems to work for me!

And oddly, it will fine for a week or two and then all over again!

Re: GAV Setting
 

Re: GAV Setting
 

Like mentioned above, each of my cars run with different GAV settings with the carbs I have on them now. In the last few months I have rebuilt a few carbs. After testing them on my A, I find that each carb will have a different GAV setting on the same A. So don't worry about where it is set, just set it so that you rig runs the way it should.

Re: GAV Setting
 

Thanks to all for responding! I read a lot of good info and ideas.

Re: GAV Setting
 

Sadly, if there is a knob or a screw slot, just can't help thinking just one little tweek will make it better, and then the DON'T DODDLE words echo in my head!