The Ford Barn

apbright · 03-15-2022, 01:00 PM

I have a Model B carburettor for which the GAV does not seem to work correctly. The carb. runs rich independent of whether the GAV is fully closed, fully open, or anywhere in between (it is running at 10 ~ 11 as measured by an A/F meter independent of the GAV position).

Off the car, I notice that the GAV position has no impact in the flow of air through the relevant passages. This leads me to believe that the GAV needle end-tip is not properly sealing against the housing. Would anyone know how to repair this?

MAG · 03-15-2022, 05:04 PM

Vince Falters site Model A & B Ford Garage has a detail drawing on the Zenith B carburetor.
The Zenith B Carb. GAV does not seat against the casting like a Zenith A carb does.
The B carb has a brass disc with a compression spring under it that provides a seat for the GAV. Disc B9531, Spring B9526.

Oldgearz · 03-15-2022, 05:51 PM

You may also or only need a new needle valve. Suppliers (I think Synder's) has them for the model B. I put a new needle in my B and it works fine. I was not wanting to mess with that little seat.

AL in NY · 03-15-2022, 06:20 PM

Depending how long ago the passages were cleaned, the area right under the brass GAV housing usually gets pretty rust impacted because of the disc and spring. I would first pull the brass GAV housing and clean under it. The GAV allows more gas to enter the carburetor after the cap jet and exit at the comp jet.

apbright · 03-17-2022, 12:22 AM

@MAG: Thanks for that tip. I had been wondering what the spring-looking-like thing was in the pictures on Vince F.'s website... had thought it was a thread, turns out it's a, uh... spring, duh..... I'm guessing my carb-in-question is missing that spring part, as the GAV turns with much less friction than other Model B carbs I have... so little friction in fact that vibration of driving down the road can cause it to change position.

I have ordered replacement set(s) from Renner's corner; the large parts suppliers do not seem to carry this part. Renner has gone quiet recently - here's to hoping his website is more than a zombie page.

PotvinV8 · 03-17-2022, 03:21 AM

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Was in contact with David at Renner's Corner back in December. I would think they're still up and running barring any tragedy. Great guy and a great source of info!

apbright · 03-21-2022, 08:01 PM

Parts arrived from Renner's corner exactly as ordered. My reports of their demise are greatly exaggerated.

Ed in Maine · 03-22-2022, 03:43 PM

You should also look at the 1932 Dealer Bulletins on the GAV. The GAV is used differently on the Model B Carb. It should be open for cold startup and initial operation but then closed. Dealers back in 1932 were getting many complaints about poor mileage, hence the special bulletin. Ed

03-15-2022, 01:00 PM	#1
apbright Senior Member Join Date: Dec 2012 Location: San Francisco, CA Posts: 169	GAV on Model B Carb INOP I have a Model B carburettor for which the GAV does not seem to work correctly. The carb. runs rich independent of whether the GAV is fully closed, fully open, or anywhere in between (it is running at 10 ~ 11 as measured by an A/F meter independent of the GAV position). Off the car, I notice that the GAV position has no impact in the flow of air through the relevant passages. This leads me to believe that the GAV needle end-tip is not properly sealing against the housing. Would anyone know how to repair this?

03-15-2022, 05:04 PM	#2
MAG Senior Member Join Date: May 2010 Location: Austin, Texas Posts: 925	Re: GAV on Model B Carb INOP Vince Falters site Model A & B Ford Garage has a detail drawing on the Zenith B carburetor. The Zenith B Carb. GAV does not seat against the casting like a Zenith A carb does. The B carb has a brass disc with a compression spring under it that provides a seat for the GAV. Disc B9531, Spring B9526. __________________ I noticed the harder I work the luckier I get!

03-15-2022, 05:51 PM	#3
Oldgearz Senior Member Join Date: Aug 2020 Location: Sagle, Idaho Posts: 359	Re: GAV on Model B Carb INOP You may also or only need a new needle valve. Suppliers (I think Synder's) has them for the model B. I put a new needle in my B and it works fine. I was not wanting to mess with that little seat.

03-15-2022, 06:20 PM	#4
AL in NY Senior Member Join Date: May 2010 Location: Southern Upstate New York Posts: 1,160	Re: GAV on Model B Carb INOP Depending how long ago the passages were cleaned, the area right under the brass GAV housing usually gets pretty rust impacted because of the disc and spring. I would first pull the brass GAV housing and clean under it. The GAV allows more gas to enter the carburetor after the cap jet and exit at the comp jet. __________________ AL in NY

03-17-2022, 12:22 AM	#5
apbright Senior Member Join Date: Dec 2012 Location: San Francisco, CA Posts: 169	Re: GAV on Model B Carb INOP @MAG: Thanks for that tip. I had been wondering what the spring-looking-like thing was in the pictures on Vince F.'s website... had thought it was a thread, turns out it's a, uh... spring, duh..... I'm guessing my carb-in-question is missing that spring part, as the GAV turns with much less friction than other Model B carbs I have... so little friction in fact that vibration of driving down the road can cause it to change position. I have ordered replacement set(s) from Renner's corner; the large parts suppliers do not seem to carry this part. Renner has gone quiet recently - here's to hoping his website is more than a zombie page.

03-17-2022, 03:21 AM	#6
PotvinV8 Senior Member Join Date: Jul 2018 Location: Los Angeles Posts: 114	Re: GAV on Model B Carb INOP Sponsored Links (Register now to hide all advertisements) Was in contact with David at Renner's Corner back in December. I would think they're still up and running barring any tragedy. Great guy and a great source of info!

03-21-2022, 08:01 PM	#7
apbright Senior Member Join Date: Dec 2012 Location: San Francisco, CA Posts: 169	Re: GAV on Model B Carb INOP Parts arrived from Renner's corner exactly as ordered. My reports of their demise are greatly exaggerated.

03-22-2022, 03:43 PM	#8
Ed in Maine Senior Member Join Date: May 2010 Location: Washington Cty., ME or Flagler Cty., FL Posts: 1,106	Re: GAV on Model B Carb INOP You should also look at the 1932 Dealer Bulletins on the GAV. The GAV is used differently on the Model B Carb. It should be open for cold startup and initial operation but then closed. Dealers back in 1932 were getting many complaints about poor mileage, hence the special bulletin. Ed