carburetor

[tudor7]

I have a 1930 Model A with a Zenith B carb. My problem is when the car
points downward, small hill, driveway, even when I brake a little hard. It
wants to stall out (gas moving forward in the carb) every time. Even just
sitting on a downward slope it runs rough, on flat ground runs great!!! Up
hill is just fine also.

This is what I have done:
1 Starts fantastic (ice cool or hot)
2 Incredible responds when you hit the gas pedal
3 rebuilt, cleaned all ports, jets replaced gaskets
4 raised, lower float level (by added or subtracting gaskets)
5 all new gas/air filters and lines
6 my gas level in the bowl is about 5/8 below the split of the carb,
(checked it with a clear tube)
Any helpful ideas???

[Rob Doe]

I have a stock model A Zenith. It idles at 470rpm with the advance 25 percent. (2 or 3 notches from where engine is timed. Base idle was set with a digital tachometer. The base idle is set with full retard to TDC and 1/4 turn open on the GAV. I've also seen 1/8 turn GAV recommended. The car should idle nice and slow at base idle setting. 350-400??

If you idle is too fast, the GAV and the cap jet have too much authority. Slow things down and then enrich the Idle Air Adjustment screw by turning clockwise. This worked for our 31 coupe. Idle Air screw is at 1-1/4 turns. I cannot force the car to stall...and I've tried multiple times.

I'll be interested in what more experienced barners post on this topic.

[Chuck Sea/Tac]

Which B carb do you have? The B 1 has a round idle nozzle in the center of the throat with a slot in line with it on the throttle plate. It also has a barrel float, although floats are interchangeable. The B2 has a slit idle orifce 20° off center and solid throttle plate.It has a semi rectangular float with a spring assist and a baffle. I run my B2 without the spring or baffle.

[Ivan in southeast va.]

Are you using a B manifold?

[Joe K]

Vince over at https://www.fordgarage.com/pages/zenithBcarb.htm discusses the various "off the shelf" Model B type carburetors. Your Model A is not the first to have had a transplant.

There were differences intentionally done to "adapt" the B carb to the Model A, the difference being primarily the lack of a fuel pump on the A.

Joe K

[mcorrell]

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Mine did that until I raised the float height so that the float is about level with the split in the carb body. I had it set to 5/8" from the split but in my case the float was way too low. Fuel would slosh forward during stops or down hills away from the jets and passages that get fuel into the throat. The float being level with the split in the body is what is shown in original drawings. This is not what most web sites say but it worked for me.

[AL in NY]

I run my B2 with the top of the cap and main jets at the same height and 3/8" below the top surface of the bottom half of the carburetor. My float is set at 3/4" at the front seam farthest from the needle and seat. The rear seam of the float set at 5/8". I don't use the baffle and spring. No stalling, no drips, easy starting and very good throttle response.

[tudor7]

How do you tell the difference between a Model A manifold and Model B manifold?

[Ivan in southeast va.]

The most visible difference is, the model B intake is flat right above where the carburetor is attached.

[Joe K]

Originally Posted by Ivan in southeast va.

The most visible difference is, the model B intake is flat right above where the carburetor is attached.

The other difference between the two intakes are Model A = 1" ID, Model B = 1-1/8". The mounting flange of the Model B is "twisted & turned" also to properly orient the Model B carburetor in its Model B application. The twist can be seen holding the manifold "level" between the holes leading to the engine block.

More Vince/Fordgarage describing the differences at https://www.fordgarage.com/pages/Bintakevariation.htm

Many have used a Model A manifold but "reamed out" the interior passage that can be reached to 1-1/8." The segment beyond the "split" can't be changed but probably isn't in the actual Model B intake either.

Joe K