B carburetor on A?

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David R.

Senior Member
My AA has a fresh rebuild, bored .080 over with a touring grind cam and Snyder’s 6:1 high compression head. Would I gain anything by boring out intake manifold and running a B carburetor. Would it be worth the trouble?
 
I have the Model B carb and matching bored intake on my '30 Roadster along with a Brumfield head and I can definitely tell a difference in overall acceleration compared to the stock setup. I would think your heavier AA would benefit from that same combo. You can have the stock intake bored or buy one from one of the vendors that has already been bored for you.
 
I have never understood why Ford did not pay more attention to flow through the intake manifold. The right angle bend at the top restricts flow. The air crowds the upper wall due to the momentum of the air which has the effect of choking off the air flow. Maybe the 40 horsepower was thought to be enough after the 20 horsepower of the Model T.

Update: The larger bore in the center tube would help with the transition to the horizontal tubes. This may be the larger effect rather than reducing pressure drop in the center vertical tube.
 
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David R. said:
My AA has a fresh rebuild, bored .080 over with a touring grind cam and Snyder’s 6:1 high compression head. Would I gain anything by boring out intake manifold and running a B carburetor. Would it be worth the trouble?
Click to expand...

Definitely worth the trouble. The B carb has larger diameter throttle bore and together with the enlarged intake runner allow the engine to breathe better, good for several HP.
 
Thanks for the feedback guys. I have a couple spare intakes I can experiment with and a good B carburetor. I’ll go through the carburetor when time permits. I have all the specs on Zenith model A carb but not on B. Perhaps someone knows where to find info on the B carburetor, flow rates for jets etc.,.?
 
Below are some photos of the model A manifold with a model B gasket.

Notice when the bolt holes are lined up how the cast center hole is off center.
USE the bolt holes to line up the gasket NOT the center hole.

This is typical, it is called core shift or casting float.

When you remove / grind the cast iron it might look like you are off center but using the bolts to locate you will actually be truing up the center hole with the carburetor.

You will only need to chamfer the center hole 3/8" to 1/2" up the runner to gain 98% of the power gain.

The STEP in diameter creates circular turbulence and is terrible for flow, the reduction in diameter from the flange to the runner split is not as important.
Getting rid of the turbulence is the most important part.

I have seen many times people enlarging the manifold runner all the way to the split and later having the carb mounting flange break off because the boring or drilling all the way up, weakened the manifold.
 

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Thanks Renner, expert advice is appreciated here. Reading the ditching air maze thread I am amazed at the number of people who are blissfully and adamantly ignorant. For some folks facts evidently have no merit when you are sure your opinion is always right. Heating and cooling have been part of my livelihood for a long time so I understand turbulence.
 
Yes, it is possible to use a 1932-34 model B manifold.
They are getting very hard to find and often require re-machining the mounting flange to the engine block surfaces because you're mixing manifolds.

Lastly, you must either modify the manifold mounting holes or get special bolts to turn the carburetor back in line parallel with the engine so that your choke rod will lineup.
The model B carburetor 2 bolt mounting flange was turned 7° to accommodate the air silencer.

I make special bolts and fuel line adapter fittings to make putting a B carburetor on a model A an easy job.
 

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RENNERS CORNER said:
Yes, it is possible to use a 1932-34 model B manifold.
They are getting very hard to find and often require re-machining the mounting flange to the engine block surfaces because you're mixing manifolds.

Lastly, you must either modify the manifold mounting holes or get special bolts to turn the carburetor back in line parallel with the engine so that your choke rod will lineup.
The model B carburetor 2 bolt mounting flange was turned 7° to accommodate the air silencer.

I make special bolts and fuel line adapter fittings to make putting a B carburetor on a model A an easy job.
Click to expand...


I was able to find a B intake at a swap meet last year. I’ll be ordering those items from your site.

Thank,

David Serrano
 
I have a B carb, and manifold on my A. IB-330 cam, Brumfield head. When I get the pedal all the way down it's like the thing does better if I let up on the accelerator just a little after the sped comes up. It's like I can't get that last little 5% out of my B carb.

Is is possible my compensator jet is too small? I mean if it is, will that keep me from feeling the full affect of the power jet tube on my car? And yes all the jets and passages are clear, inclding the one around the collar of the power jet tube. The little `3/8" jet at the bottom of the float well, adjacent to the power jet tube?
 
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Gene F said:
I have a B carb, and manifold on my A. IB-330 cam, Brumfield head. When I get the pedal all the way down it's like the thing does better if I let up on the accelerator just a little after the sped comes up. It's like I can't get that last little 5% out of my B carb.

Is is possible my compensator jet is too small? I mean if it is, will that keep me from feeling the full affect of the power jet tube on my car? And yes all the jets and passages are clear, including the one around the collar of the power jet tube. The little `3/8" jet at the bottom of the float well, adjacent to the power jet tube?
Click to expand...

Well, unless you have flow data on your carburetor jets, we will forever be guessing.

I suggest you have someone flow test your jets and compare the data to the flow number I use for todays fuels.
Or I have flow tested sets for sale

Trouble shooting the carburetor should be done methodically and logically using proven methods, no guessing or youtube entertainment.

I have loads of information on the Model B Zenith carburetor I would be glad to share.
Visit my website rennerscorner.com to get my email address and send a request for B carb info.

PS the compensator jet and power jet are 2 separate circuits that don't rely or work with each other, but if one of those 2 jet was undersize or their pathways obstructed then this could limit the top end.

David
 
Gene -
Also check that your accelerator linkage pegs at full throttle on the carb. Switching from carb to carb usually requires some tweaking of the long accelerator arm to ensure the linkage makes full travel. Have someone sit in the driver's seat and with the engine off, you watch the linkage action as the accelerator button is pressed to the floor. Make sure the butterfly arm on the carb pegs at full throttle.
Even switching from one Zenith to another Zenith might require bending that long arm to achieve full throttle. These carbs and linkages have had a lot of owners in the last 98 years and who knows what has been done to them during that time?
Marshall
 
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