Modify B Carb on Model A

G

Gino

Senior Member
Hi, found a “B” carburetor in my stuff. Anyone know how to modify it so it will fit on the A manifold? As I understand I will have to do adjustment to the bolts. And ream the intake a bit. Thanks for the help
 
B carb installed on a A manifold does not require ANY modification.
B carb installed on a B manifold on A engine does require the modified bolts.
The B manifold puts the carb at an angle causing poor alignment of the choke rod. Snyders P/N B-9510-S (Choke Adapter Kit).
If you use these bolts make sure they are not too long. If too long they can break the carb (front) mount. Yes, I learned the hard way.
 
MAG is correct about bolting a B carb to an A manifold. But to get all of the power the carb makes you do need to deal out the manifold vertical portion. It will work fine without the reaming you just don’t get all the benefits of the larger carb.

Mike
 
the gas inlet is on the front not the side, modify the fuel line a bit.
no long bolts, like above you will break the ear off.
you can hog out the manifold but is not needed for fit.
 
OK so here's the deal! When Henry (Et al) were increasing the HP of the "New" B engine, they realized that it wasn't breathing so well so they increased the size of the throat from 1.125" to 1.250 and they designed a new intake manifold. ( They gave it a new crank, cam, lighter flywheel and raised the compression ratio too). The increase in throat diameter will get you just under 4HP ( Not bad for a 40 engine, almost 10%) The B carb has three distinct improvements over the A carb 1) More HP, 2) The float is not affected by sudden stops, it's set at 90 degrees to the centerline of the car. Not inline as with the A carb. 3) There is an accelerator jet which the A carb doesn't have. I would suggest you go to Piranios Dyno, model A. Dennis Piranio has the figures for several modifications.
Terry

If you go to my picture album, you will see a side by side comparison of an A and B carburetor. I can't post pics, so there you have it!
 
Henry Ford himself never ever bothered with matching the carb to the inlet manifold in production . The AA truck was built in Dagenham into 1936 . They were fitted with the B carb mated to the A RHD inlet manifold which has the peg on the top for the link to the distributer . This meant there was an 1/16" "step" in the inlet tract where the B carb met the A inlet manifold . The trucks ran just fine a special larger bore inlet manifold was not produced . The AF small bore engine was fitted with a " KAYCE" carb identical to a Zenith the only difference was smaller jets and the potmetal venturi with a much reduced diameter . The throat of the KC is the same as the Zenith so the "step" is even bigger but they left the factory just like that and just run fine .I ask myself for ordinary running if you really need to ream out the A manifold Henry did not think so .

John in sunny afternoon Suffolk County England .
 
MAG said:
B carb installed on a A manifold does not require ANY modification.
B carb installed on a B manifold on A engine does require the modified bolts.
The B manifold puts the carb at an angle causing poor alignment of the choke rod. Snyders P/N B-9510-S (Choke Adapter Kit).
If you use these bolts make sure they are not too long. If too long they can break the carb (front) mount. Yes, I learned the hard way.
Click to expand...




1. Very true on B Model carbs but this is also a problem with some Model A Zeniths.


If a 1 inch bolt is used instead of the 3/4 inch some Model A Zeniths will be be broken.


This is a problem with any bolt used not just the modified bolts for use with Model B carbs.


2. Also if a Model B Zenith is installed on An Otwell Model 14 manifold heater the flange will be broken off.

But this for a totally different reason than discussed above.
 
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old31 said:
Any idea what the cost would be to bore out a A intake to a B carb specs?
Click to expand...

I used to do it, butI don't have a Bridgeport and my drill press is too small. I was charging $60 + shipplng, with polishing and a slight reshaping the bore to favor the two runners. There's more work to it than just putting a reamer in the hole. Be careful of your centering because of the wall thickness. I use a pin to locate the manifold. This way I'm centered from top to bottom. The runner is about 4" long and I believe the wall thickness is between 1/8" and 3/16" before boring. That's why I preferred to locate the manifolds with a pin, so the drill stayed on center and didn't come out the sides of the runner. I never had an accident! Once it's opened up, I believe in polishing it. There's two schools of thought on this subject. One says polish all obstructions to a slick finish for a frictionless passage. While the other says a rough finish will help with the atomization of the gas particles. Now! Your fuel gas mixture is moving in a 1 1/4" column through the runner, what happens (or doesn't happen) to the fuel at the center of the column that doesn't touch the walls? Then there's the "Golf Ball" dimples theory. Golf balls have high and low spots. This is to cause the golf balls to "ride" on the high spots. I guess it works on golf balls, but I don't know about manifolds. I do know that roughness causes turbulence and turbulence slows everything down. Good Luck with it in either case!
Terry
 
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