Model B Carb/GAV

Karl

Karl

Well-known member
On a recent post someone suggested that the GAV on the Model B carb be closed (once the car is warmed up ) for normal running rather than the normal 1/4 open. As I'm running a B Carb on my A and have just run it 1/4 open as normal am I running it to rich? I would appreciate some one ? Vince confirming what the correct GAV position is on a B Carb . Thanks Karl
 
Others more knowledgeable may correct or overrule me, but my understanding is that the Model B Zenith GAV is supposed to be closed when running, and only enrichened when starting a cold engine. My coupe with a B carb runs that way, and usually I don't have to enrichen (open) the GAV at all to start in warm weather.
Fearless
 
My old B would just barely stutter, when the GAV was closed. If I open it up a 1/4 turn it smooths right out. I think it depends on your jets, your bore, and even your cam. I have an electronic ignition, so possibly the hotter spark makes a difference as well? I guess what I'm saying is every car setup is different, and you have to find out whats right for you. Checking your plugs is one way to tell if you're rich or lean. Although I have always heard that B's run richer.
Chuck
 
I have had B-carbs that would only run well with the GAV open, sometimes as much as 1/3 - 1/2 turn open. That changed after they were stripped down, the drilling plugs removed,, and the passages cleaned out. After rebuilding, these carbs would run well with GAV closed but some were still a little too rich.

Check the number on the main jet. Sometimes B-carbs have had a Model-A #20 main jet installed somewhere along the way. Some B-carb main jets have been cleaned too zealously and the bore is too large so it flows too much fuel at all speeds. You may have to solder and rebore the jet tips to give a flow rate of 145 ml/min using the apparatus described in some of the books and on the web. I have also found "B" cap jets to be all over the place with flow rates ranging from 140 ml/min to as high as 480 ml/min., so this is another thing to check. A good B-carb will give 20-21 miles per gallon on a good engine. But some just never seem to do better than 14 mpg no matter what you do.
 
According to the instruction manual for my 4 cylinder 1932 Ford "The valve should be turned back (clockwise) as soon as the engine has become warm. The engine should never be operated with this adjustment open".

Charlie Stephens
 
Thanks guys. Seems to run fine with GAV closed . So will use this setting in future
 
I run mine closed. I open it up to 1/4" turn when starting. But not for long and just in the winter.
 
Hi. i have a B carb on my "A" i have to have the gav open 3/4 turn, or it tries to stall when i take my foot off the throtle, if closed or 1/4 open. thanks Pete
 
I run my B carbs with the GAV closed. When first cranking in cold weather I open the GAV 1/4 and sometimes 1/2 turn or it will hesitate. If run with the GAV open after warm up will result in sooty spark plugs and in worse cases diluted crankcase oil.
 
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