Running a Model B Carb on a Model A

[Kevin - Illinois]

Are there any advantages to running a B carb on a Model A? More power, no stalling at sudden stops, better idling???

Thanks,
Kevin

[Fred K-OR]

I have run a B carb on my huckster since I restored it. There is a place down in TX that has done some test on the B carb. Web site is www.modelaparts.net. On one of their test, just putting a B carb on a stock A engine and manifold at 2200 RPM it did not show much of a change in HP. But when they modified the manifold, (I think they bore it out) it picked up a some HP. You may want to check their web site or call them.

[Karl]

I've run both and currently am running a Model A carb. I am told that the Model B carb is worth a bit of extra horse power but I never noted any difference to my well set up Model A Carb. If you do use the B you need to open up the inlet on the inlet manifold to get max performance as the B carb has a larger diameter outlet Karl

[2manycars]

I have on on my tudor, and I think it runs better and makes more power. The design is different than an A zenith. I have it on a stock A intake, but am told it will run better with the intake bored to B dimensions. The B intake is only 1/16th inch larger, so I am not convinced it makes much difference except at wide open throttle, but I just made a jig for my bridgeport so I can bore the intake to B specs. I did one, and it turned out ok.

[TinCup]

One of the big advantages is the float design. They are not as prone to stalling at a quick stop because the float is mounted sideways. As others have said the manifold has to be honed to get the best performance from the carb.

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http://www.modelaparts.net/dynosheets.htm/dyno1.htm
http://www.modelaparts.net/dynosheets.htm/dyno8.htm

Here is the results of dyno testing of a Model A engine with different combos of Zenith A or B carbs and stock or modified manifolds. It shows in their testing that a Model B doesn't perform quite as well as a Model B at ~ 2000 rpms for HP.

But with that being said, I personally have been running a B carb on my 30 tudor for a couple of years and I like it. Stock Model A sized manifold.

I never had a problem with using Zenith A carbs but it seems in my own driving experience that I have more hill climbing power with this particular B carb over the A carbs I have tried before. On hills where before I would be forced to downshift to make it to the top, I now have just a little more umph to make it to the top with gas pedal to spare.

This Model B carb I can run typically with the GAV closed all of the way. I get good MPG compared to other Model As on our tours and the spark plugs burn tan in color. I have a collection of Zeniths and Tillotsons that I have used on this car over the last twenty years and this B is my favorite..... Maybe it is just a good carb with the correct sized jets so your experience maybe different...

Also if you ever go to a dual updraft carb setup with the dual manifold you can only use the Zenith B or the Tillotsons because the GAV needs to closed or left alone on the front carb. Look at Purdie's set up.

[Kevin - Illinois]

Thank you all for your responses! I'm going to try one!

[George Miller]

Originally Posted by Kevin - Illinois

Thank you all for your responses! I'm going to try one!

If you do not want to bore out the intake. You should blend the step where the carb bore meets the intake bore. So you will not have a sharp step there.

[Richard Lorenz]

The B carb also has a power jet that enriches the fuel/air mixture when the throttle is above about 2/3 open.

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I also have on my particular car setup the Model B 90 degree plumbing for the standard Model A fuel line. This way if I never need to quickly swap out my carb for a spare Model A Carb it is done with no mussing with swapping out with a custom fuel line.

It is hard sometimes to source this plumbing from your local big box stores or even some local hardware / autoparts shops. But some of the Model A vendors sell a Model B adapter kit to use that has the large copper gasket, modified mounting bolts to allow for a slight turn to align the choke rod better, and the brass 90 degree fittings. Here is a pix that I grabbed off of Mike's Affordable website.

Please let us know how your experience is when you get your Model B carb on your car.

Model B carb setup.jpg

[Purdy Swoft]

You may gain a little top end But will feel no change in low end. I hand ream the model A intake manifold to B size. For a real noticeable boost, the B carb works best with higher compression and at least the B cam. Dyno tests show that the C head gives nearly seven HP. The B cam, larger manifold and carb give nearly three more Hp. They all work together to give the B engine ten more HP and an additional 600 RPM. Don't expect a big boost by using a B carb alone with no other mods.

[Charlie Stephens]

This may be a dumb question but why not just run a Model B manifold?

Charlie Stephens

[M2M]

Are good B carbs easy to find? Where's a good place to buy or look for one? What sort of price do they change hands at?

[Purdy Swoft]

Here is a pic of the dual updraft B carb setup on my speedster. This is a cast iron manifold with larger runners than the model A manifold. No boring or reaming was needed on this manifold to use B carbs. Old cast iron manifolds like this one isn't easy to find. The new repro dual updraft manifolds are all made of aluminum and the intake runners are model A size. I feel that the lighter Tillotson or Marvel carburetors would be best to use with the weaker aluminum manifolds.

I run my model B carbs with the GAV closed after warm up. It was easier for the choke rod to connect to the front carb. I use the front carb for choking and GAV adjustments. I keep the GAV closed all of the time on the rear carb, this would hold true no matter what carbs that I choose to run. When cold, the B carb will hesitate. I run the front carb i/4 to 1/2 turn open untill warm up and then close the Gav completely. I run dual B carb updraft setups on two of my model A's and both get better MPG than the ones that run a single Zenith. I think that this is because of better distribution bacause each intake port has a carb. You don't have to mash the accelerator button nearly as far to go twice as fast. When the accelerator button is mashed to the 2/3 open point and both high sped jets kick in you can really feel the power surge . Even with a dual carb setup, you need a higher compression head for best results.

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Here in the US there seems to be plenty available at most local swap meets and most of the jet / gasket replacement parts are available from the Model A vendors. It seems to be hard to find any missing Model B carb mechanical parts like choke plates / shafts etc.. The top mounting flange is not as beefy as the Zenith Model A carbs so the tops are seen often with broken, or repaired flanges. Seen lots of lower body parts out there as well with no tops.

Try putting a request in the Ford Barn Swap meet section and see what the FB members may have available to sell.

Also there is always EBAY and buyer beware..... With a quick search on EBAY I found several for selling right now. Here is one that is representative of what you will see available.

http://www.ebay.com/itm/181020145121...84.m1438.l2649

Please check out the Model A Ford Garage site of Vince Falter's http://www.fordgarage.com/ as he shows all of the different 1932 -1934 flavors of them as well as being a EBAY part supplier for the often missing or broken power jet tube.

[jrapose]

I have one on my motor and I like it....what I did was grind out the inside of the manifold using a sanding disk I bought at Harbor Freight....it was easy and quick...the manifold is soft cast iron and sanded like soft wood....probably not perfect but all you need remove is a 1/16" and that was easily done in less than an hour...total cost was about $8....I guess you could use grinding stones or a power hone just as well.

Joel
Chester Cal.

[Terry, NJ]

I've bored a couple of manifolds out. At this time, I can't give you figures or results, but the boring is relatively easy to do...... If you have a Bridgeport or similar machine. I would not try it on a drill press without a jig. And it would have to be a large one. The hardest thing about setting it up is that the bore/port is not square with the flange. You'll need a locating pin pretty close to the dia. of the bore about 4" long. This pin should be a standard nominal size on one end, that will fit in a collet. Use this pin to locate with. By using this pin you can maintain concentricity from top to bottom. Lock it down on an angle plate and your ready to drill/bore. because of the 3 deg angle of the flange. start the drill very slowly as it will contact the high side first and it will push off slightly. Once you have 100 % contact of the drill around the hole. you can start to drill with a little more pressure until it bottoms out. I have used 1 1/4" (1.250") with good results. You'll note that the walls are getting very thin and you don't want it to crack off. When you're done drilling, run an 1.5 inch flap wheel through it to smooth the rough machined surface. I was told don't bother polishing it, that it doesn't do any good. Good luck!
Terry

[SteveB31]

We have some nice rebuilt B carbs for sale and several NOS B carbs still in the original boxes. Also have some not rebuilt ones as well.

Steve Becker
Berts Model A Center

[SSsssteamer]

For my B carb, I placed the B carb gasket on the manifold and I used a carbide burr in my air die grinder to remove the excess metal extending beyond the gasket hole. It was cleaned out in about 3 minutes at no cost but time. When buying both A or B carb rebuild kits, don't use their jets unless yours are damaged or missing. The jet sizes in their kits are usually wrong as the Chinese have poor quality control. I use an H & H built up touring motor. With it's modifications and the B carb, it has easily 20 more horse power. With my 3.54 rear end, the '30 touring easily climbs most hills in high gear and it cruises safely at 65 mph. It is more friendly at 60 mph than 65 mph.

[Tom Foster]

I have a B carb on an undrilled A manifold, with 5.9 compression and a touring cam from Pete's in Albuquerque. With a lightened flywheel it turns 3500rpm at hillclimbs and idles nicely. When I changed back to an A Zenith for a while I noticed a power loss with less top end.
Fearless