Model a vs b carburator

C

cfordman

Member
Ive got a stock A motor with a B distributor. having a choice between a model A zenith carb and a model B carb for the same money will there be any noticeable improvement by going to the B? Thoughts?
 
It appears your question involves three (3) things; i.e., money, improved performance, & choice between an A or B carb:

I would guess you would be happy with the B, not because of money, & not performance which will not be much better with a stock A engine; however, because of your interest in performance, if you have the B carb, & later try out an enlarged A intake, with a higher compression head, & a higher lift cam, you will be glad you chose the B carb.

Just a guess.
 
I agree. You may get a small increase in top end with the B carb if it has the large venturi but you won't feel the difference. You will need higher compression, either a model B intake or a reamed out model A intake and probably a better cam to feel any real improvement as Mr. H.L. says above .
 
I don't know if this is any indication of the good or bad features of a B carb but it is just my observation so far with the B carb on my huckster. The B carb has been on my rig ever since I owned the chassis. When I converted to the huckster body, the engine rebuilder left the B carb on the motor and rebuilt it also. My huckster weighs about 2700 pounds, a little heavy for Model A's. The huckster has everything stock except for the B carb.

So what I have found is that with the huckster (with the B carb) I get about 15 or 16 MPH. While with my coupe which is also all stock and has an A carb, I get about 20 to 21 MPG. What I had planned to do is put an A carb on the huckster and then check the millage again to see if it makes a difference of not. Have not done this yet so don't know if the lower MPH on the huckster is due to the B carb or the weight of the huckster

Sorry I don't have better info for you at this time but just thought I would share for what it is worth. Maybe others on the Barn have had similar experiences and can comment.
 
Purdy, One if the simplest mods you can do is to bore your intake to B specs. I use a 1.250" drill in a Bridgeport. It can be done with an angle plate on a drill press too. The Bridgeport is better, but..... Go the full length and then polish it with a 1 1/4" flap wheel. It may take as long as a half a hour. Whoa...,wait You'll need a locating Pilot that fits in the chuck, about 1 3/16 dia. and 2 1/2 or so long. Sorry about that! As long as the manifold is off, put some polish on the intake ports too. With either the A or B carb, you'll feel some difference, but more with the B. My own A has a rebuilt (about 3 years old) Zenith A carb. When I switched to the B, I got some idea what it would be like if it were running good. One of these days, I'm gonna bore the air intake out .020-.030 or more of a B carb. (They're pretty thin) and see if I can make some real difference. But I'm looking at a tough setup and a lot of time on the lathe. For now I just want it to run.
Terry
 
Terry, I'm a po country boy and don't have a Bridgeport lathe. I've been using adjustable reamers to enlarge model A manifold runners to model B size. Its a slow process but works. I've noticed a gain in top end with a stock model A engine with a B carb and reamed out intake. I used a die grinder to enlarge and smooth the intake ports on the engine in my roadster. I also enlarged and smoothed the area under the intake valves. I didn't polish the intake ports because I'm told it can cause the gas to deatomize in a flathead engine. I smoothed the rough cast in the exhaust ports and under the valves but didn't enlarge the exhaust ports for fear that it could hurt the low end torque. I run a 3/4 race Winfield cam and Brumfield 5.9 head with a lighter model B flywheel. I run a cast iron Trojan intake manifold with dual model B carbs. I did a few minor mods to the original distributor and use a Pertronix flamethrower coil. I also completely gutted the muffler to eliminate back pressure. With these mods I can really feel the power when the high speed jets cut in on the B carbs. This has been a smooth and dependable engine . The engine idles good but not as slow as a stock engine with heavy flywheel but we are happy with the performance. It runs about like a modern car and we can accellerate going up hill if we want to. My wife drives it most of the time and we drive it to car shows instead of trailering it like many do. I can even hand crank it with ease. I did it all myself and can't help but be proud of it. Though I've posted it a bunch, here is a pic of our engine.
Jam784.jpg
 
In the old days, every body knew that: (pi r square) was used to find the areas of a circle.

Today with modern math, pies are round & not square; so nobody can find the area of a circle or even imagine a 17 trillion dollar loan with nobody paying for it.

We really have a modern political agenda today to establish & maintain total dummies. What ever happened to arithmetic?

The Model A carburetor & intake had a 1" diameter throat & the Model B had a 1-1/8" diameter throat.

With (pie are round) in lieu of (pi r square), nobody with new math can calculate that this 1/8" larger diameter for a B carburetor is actually a 25% increase in area of fuel/air entering the combustion chamber.

Wow! Arithmetic, what is that?
 
No one mentioned that the B Zeniths float bowl is shaped differently and the float hinged on a different axis so that you don't get that annoying stumble sometimes when you stop quickly. That also is an advantage. Its just an improved design.
 
I imagine it climbs hills quite well! I was warned off the polishing also. No reason given. Just clean up any casting glitches and leave the surface a little rough. So I used the word "polish" kinda loosely! I've been wondering if a little reshaping of the top of the valve guide "tower". Would this improve the flow?
Since you're not taking much out of the manifold 1/32 - 1/16 the reamers probably work fine.
Terry

Purdy Swoft said:
Terry, I'm a po country boy and don't have a Bridgeport lathe. I've been using adjustable reamers to enlarge model A manifold runners to model B size. Its a slow process but works. I've noticed a gain in top end with a stock model A engine with a B carb and reamed out intake. I used a die grinder to enlarge and smooth the intake ports on the engine in my roadster. I also enlarged and smoothed the area under the intake valves. I didn't polish the intake ports because I'm told it can cause the gas to deatomize in a flathead engine. I smoothed the rough cast in the exhaust ports and under the valves but didn't enlarge the exhaust ports for fear that it could hurt the low end torque. I run a 3/4 race Winfield cam and Brumfield 5.9 head with a lighter model B flywheel. I run a cast iron Trojan intake manifold with dual model B carbs. I did a few minor mods to the original distributor and use a Pertronix flamethrower coil. I also completely gutted the muffler to eliminate back pressure. With these mods I can really feel the power when the high speed jets cut in on the B carbs. This has been a smooth and dependable engine . The engine idles good but not as slow as a stock engine with heavy flywheel but we are happy with the performance. It runs about like a modern car and we can accellerate going up hill if we want to. My wife drives it most of the time and we drive it to car shows instead of trailering it like many do. I can even hand crank it with ease. I did it all myself and can't help but be proud of it. Though I've posted it a bunch, here is a pic of our engine.
Jam784.jpg
Click to expand...
 
Terry said:
I imagine it climbs hills quite well! I was warned off the polishing also. No reason given. Just clean up any casting glitches and leave the surface a little rough. So I used the word "polish" kinda loosely! I've been wondering if a little reshaping of the top of the valve guide "tower". Would this improve the flow?
Since you're not taking much out of the manifold 1/32 - 1/16 the reamers probably work fine.
Terry
Click to expand...

Terry, I have never thought about reshaping the upper valve guide. It seems that it may help flow but I haven't tried it.
Purdy.
 
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