Model B Carb Issues

TinCup

TinCup

Well-known member
So as one of my Covid-19 therapy projects I rebuilt and restored 2 Model B Zenith Carbs. I actually really like them. They run and idle well and the transverse mounted float helps with stalling at sudden stops. Both of these perform almost the same and both have the same quirk. From start to about 180 degrees engine temp they perform flawlessly. Once the temps get up the carb stutters when taking off from a start and require more GAV adjustment. I was surprised because before the summer temps hit I had driven these carbs many miles with no issues. I start the car with about a quarter turn of the GAV and almost closed after the car warms up. If the car temps stay below 180 it will run all day like this. After the temp starts to exceed 180 then it acts as if it starved for fuel and I must open the GAV at least a half to three quarters of a turn to get it to smooth out. Stock A Zenith we all start with a quarter to a half open and then close as the car comes to temp. If I run a stock A Zenith this behavior is not repeated.
 
So your B carbs don't like hot weather? I installed a B carb on a Model A last year and like it. Like yours, it starts and performs well at all speeds. We took the car shopping a week ago when it was pretty hot outside. It ran fine, but one time at a gas station, it was a bit hard to start. I had to crank on it for several seconds. I like to barely touch the starter button and it's running. The other two times I started the car, it did start instantly.
We had a severe vapor lock problem on hot days a few years back with a 35 Ford. I filled it up at the next gas stop with premium gas. Premium gas absolutely fixed the vapor lock on that car.

Just a wild suggestion, but you could fill your Model A with Premium gas the next time you gas up and see if that makes any difference in how your B carbs behave in hot weather.
 
I have a B carb with bored out intake and no issues with hot weather.

I use a K&N Filter and 4 oz MMO per 10 gal gas.
 
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Try running pure gasoline without alcohol in it. Buc-ees near us sells it. Or places that cater to boats.

:cool:
 
Good Morning...We run a B carburetor on our A and have no trouble in Arizona's summer heat. We run 87 gas with Marvel Mystery Oil...we have to set the gas adjustment valve at about 3/4 open to keep the engine happy. We do run a K & N air filter and the old girl does run a bit rich. We don't have flow tested jets...I don't mind the bit rich as the car runs cool and happy. PS...when the weather is over 95 I don't drive it much after about eight in the morning, as I don't like weather that hot...for that weather I just jump into my Jeep. Ernie in Arizona
 
Try a phenolic spacer between carb and intake. I also put a piece of metal that acts as an insulator between the carb and exhaust manifold. You’d be surprised at how hot the carb gets, which causes some vaporizing of the gas.
 
The GAV on the Model B Carb is used differently from the Model A. Per the Service Bulletins, Ford stated that the GAV is only used when the car is cold. Then the GAV should be closed. The Service Bulletiin stated that when customers complain about gas mileage they should be urged not to have the GAV open. Therefore, if the GAV is necessary after the car has warmed up, it may mean that the jets are not sized per the specifications and should be flow tested. Refer to Steve Pargater's manual on restoring A and B Carbs.
 
Looking at the sectional view of the Model "B" carb in the 1932 Service Instructions, heat would raise the fuel level in the float bowl, and this would cause the fuel to overflow the Main Jet and the Compensator Tube which are situated in the Venturi. Try lowering the fuel level a bit.
 
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