Downdraft Carb suggestions

[my2nd40]

I want to put a downdraft carburator on my stock model a engine. Which one should I look for? 81,97 or 94, and what is the best way to set it up?
thanks

[V4F]

a weber ! best by far .......

[BRENT in 10-uh-C]

Originally Posted by my2nd40

I want to put a downdraft carburator on my stock model a engine. Which one should I look for? 81,97 or 94, and what is the best way to set it up?
thanks

While the 81 will be closest to cubic inch size of the Model-A engine, most folks often find they are still too large for a stock engine. More cam and larger valves allow for the 81 to be more useful, and more compression allows the additional fuel to become more useful. My personal experience for a stock engine, all of those downdrafts are a tad too much. If you are adamant you want a downdraft, there were some Bendix manifolds made to adapt the Rochester single BBL carb found on engines such as the 216 ci Stovebolt engine from the 30's.

Just out of curiosity, have you considered installing a Model-B carburetor & manifold for a little more airflow? With those, there is not a need for plumbing in a fuel pump when used on a Model-A.

.

[racer32]

Is there a quick way to ID the B manifold? Headed to a swap meet today.

[kelley's restoration]

Originally Posted by racer32

Is there a quick way to ID the B manifold? Headed to a swap meet today.

its flat on top compaired to a model a which is rounded
tk

[jkeesey]

Sponsored Links (Register now to hide all advertisements)

I use a 97 just because its the best carb I had around. It does run a little rich but its not too bad. Still gets about 20 miles per gallon.

[Jim Brierley]

I have found the opposite of what Brent says. The 81 is adequate, and better than the stock carb, but the 97 is better, and cheaper. They usually need to be totally stock but sometimes may need a slight main jet change. I've tried them all.

[CarlG]

I have a Weber on mine, and it works great. Can't compare it to any other DD, just haven't used them.

[Logan]

Stromberg 48,81,97 all run good on an A block. Of course you have to jet it correctly, but that's not hard to do. On a flat head you want the mixture to be a little rich, rather than lean. Lean will burn up a motor. People often refer to the 94 as a stromberg, but it's actually a Holley. It's he cheapest one out of all of them, but they tend to run leaner than a stromberg. I have a 48 and I love it, I had an 81 once and traded it for a weber and boy was that a mistake. The webers are fine, but the strombergs give you faster acceleration in my opinion and run better down the highway. The webers do get better gas mileage though. But not by much. I've tried most of the popular downdraft conversions, and the stromberg has been my favorite so far. You can usually pick up a 48 or a 97 in decent condition at a swap meet for about 75-100 dollars that needs rebuilding. For an 81 you can expect to give 250-300 for one that needs rebuilding, or closer to 400-500 for a rebuilt, if you can even find an 81. They reproduce the intake manifolds, and I think they're right around $200 for the manifold.

[Purdy Swoft]

I run dual updraft with B carbs. Its easy, bolt them on and thats it. I use original numbered jets. Gravity flow works fine, no pump or pressure regulator needed. This setup will run good, even on a completely stock engine. For best results with any mods on the model A, a higher compression head should first be added to really feel the improvement.

[Tiny]

Originally Posted by Purdy Swoft

I run dual updraft with B carbs. Its easy, bolt them on and thats it. I use original numbered jets. Gravity flow works fine, no pump or pressure regulator needed. This setup will run good, even on a completely stock engine. For best results with any mods on the model A, a higher compression head should first be added to really feel the improvement.

Purdy can you post some pics of that setup? It sound WAY cool.

[BRENT in 10-uh-C]

Originally Posted by Jim Brierley

I have found the opposite of what Brent says. The 81 is adequate, and better than the stock carb, but the 97 is better, and cheaper. They usually need to be totally stock but sometimes may need a slight main jet change. I've tried them all.

Ohh come on now Jim, when have you EVER had a stock engine??

[Charlie Stephens]

Originally Posted by racer32

Is there a quick way to ID the B manifold? Headed to a swap meet today.

In addition to being flat on the top there was a boss and threaded hole for the clamp that held the Model B choke cable. There were two Model B intake manifolds. The early one had a large threaded hole that was originally intended for a vacuum line to the vacuum assisted clutch that was never adopted. The later version had a vacuum line for the windshield wiper that went to the rear and would probably look better on a Model A.

Charlie Stephens

[Tiny]

The B manifold is also "clocked" a few degrees toward the motor. How do you overcome this in an A and hook up the GAV?

[Purdy Swoft]

Originally Posted by Tiny

The B manifold is also "clocked" a few degrees toward the motor. How do you overcome this in an A and hook up the GAV?

Snyders has a kit to solve this problem. Look on page A-136. Part number A-9510-K Lists for $31.00 . Its kinda pricey for what it actually is. I cut the mounting flange off the manifold, rotated it as needed and brazed it back on. Be careful if you try this. The brazing job has to be good or you will end up with vacume leaks.

[Purdy Swoft]

Originally Posted by Tiny

Purdy can you post some pics of that setup? It sound WAY cool.

Here is a view of the setup on the speedster. The manifold is a cast iron uniflow that was made in the thirties. This manifold has larger runners and performs real good. I got this manifold from Berts, several years ago.

[Purdy Swoft]

Here is a picture of the cast iron Trojan that I bought on eBay. This was taken when I was building the roadster. I've got better pics on photo bucket. Photo bucket seems to know which pictures that I want to post and most of the time won't let me. I had it working good late last night but not today. These pics are on Blue Melon. If I can get Photo bucket working again I'll post more.

[Tiny]

Thats a really neat setup. Who cares if you cant make photobucket work, if you can make two B carbs work!

For Photobucket I always use the IMG link by the way, never had a problem

[Tom Endy]

A club member recently told the membership about his misfortune with a downdraft carburetor. His Model A is equipped with a downdraft manifold, downdraft carburetor, and an electric fuel pump. His thinking was that the fuel pump would block any fuel flow from the tank to the carburetor when the engine was shut off, therefore there was no need to shut off the tank valve. Wrong assumption.

He had not driven the car for about three weeks, when he went to do so he found that about four gallons of fuel had flowed into the intake manifold and into the engine, including the oil pan.

His advice is to always shut the tank valve off. One would also hope that the tank valve has the ability to shut off 100%.

Tom Endy

[CarlG]

Originally Posted by Tom Endy

A club member recently told the membership about his misfortune with a downdraft carburetor. His Model A is equipped with a downdraft manifold, downdraft carburetor, and an electric fuel pump. His thinking was that the fuel pump would block any fuel flow from the tank to the carburetor when the engine was shut off, therefore there was no need to shut off the tank valve. Wrong assumption.

He had not driven the car for about three weeks, when he went to do so he found that about four gallons of fuel had flowed into the intake manifold and into the engine, including the oil pan.

His advice is to always shut the tank valve off. One would also hope that the tank valve has the ability to shut off 100%.

Tom Endy

Looks like a really good argument for an electric shut off valve!

[Charlie Stephens]

Originally Posted by racer32

Is there a quick way to ID the B manifold? Headed to a swap meet today.

Here are a couple of pictures in response to your request. Note large vacuum attachment boss is in front of early manifold.

Charlie Stephens

[john in illinois]

I have a new English 97 on a heated Charley Yapp manifold. It runs noticeably smoother than the Zenith. Used an air/fuel meter to check jetting. smaller jets were too lean,stock jetting was just right.

It is a little touchy to start hot. I think I will try a heat insulator betweeen carb and manifold.

Air filter in pic is too restrictive. A 4" tall K&N works good.

[Art Bjornestad]

I use an electric fuel shut off valve o a pair of 81's......keeps the "forget" part out.

[Purdy Swoft]

Originally Posted by Tiny

Thats a really neat setup. Who cares if you cant make photobucket work, if you can make two B carbs work!

For Photobucket I always use the IMG link by the way, never had a problem

I'm back on photo bucket, here is a better pic of the Trojan setup.This is how it looks now on the finished roadster. I've got one more.

[Purdy Swoft]

different angle

[gwhite]

Sponsored Links (Register now to hide all advertisements)

A Winfield S/SR would be a good period option.

[JtownJoe]

I also can vouch for the Weber set up. It was difficult to get the right throttle linkage travel range, either not fully opening or too fast at idle, but discovered some play in the two piece shaft & spring on my stock accelerator linkage but once corrected it runs very well and no longer has the constant gasoline in my attached garage. Only complaint is the chrome air cleaner supplied with it, looks tacky to me.

[BILL WILLIAMSON]

Originally Posted by JtownJoe

I also can vouch for the Weber set up. It was difficult to get the right throttle linkage travel range, either not fully opening or too fast at idle, but discovered some play in the two piece shaft & spring on my stock accelerator linkage but once corrected it runs very well and no longer has the constant gasoline in my attached garage. Only complaint is the chrome air cleaner supplied with it, looks tacky to me.

Whut's wrong with my air cleaner? I liked it! Minerva ran 80 MPH, once only! And the pizza stayed HOT by the exhaust heater
Bill W.

[Jordan]

I had a weber on my car, then I was convinced to put a stromberg on there. That was on it all summer. It was way more sensitive in pedal reaction and acceleration, but I didn't like it on the top end of cruising. It also seemed to run differently with every tank of gas. I switched back to the weber that never gave me a problem.

[Jim Brierley]

Brent, When I bought my early '30 tudor several years ago it had a stock "B" engine in it, with "A" manifolds and carb. I ran this for a very short while but during that time the Auburn hill climb was being held twice a year. At one climb I ran it "stock", meaning as I bought it. For the next climb a few months later I had installed a Winfield 6:1 head, the times improved by a full second. That same day I installed an 81 on a Burns manifold, the times improved by another full second. For the next meet I had a 97 on the same manifold, and it picked up another 3/10 of a second. These were all averages of 2 or 3 runs. Shortly after that I came back to my normal self and put an early Miller under the hood. So for me, a stock B engine is as close to stock as I ever came, you caught me!

[racer32]

Feel free to send me all those crummy old Strombergs!

[denis4x4]

Originally Posted by Tom Endy

A club member recently told the membership about his misfortune with a downdraft carburetor. His Model A is equipped with a downdraft manifold, downdraft carburetor, and an electric fuel pump. His thinking was that the fuel pump would block any fuel flow from the tank to the carburetor when the engine was shut off, therefore there was no need to shut off the tank valve. Wrong assumption.

He had not driven the car for about three weeks, when he went to do so he found that about four gallons of fuel had flowed into the intake manifold and into the engine, including the oil pan.

His advice is to always shut the tank valve off. One would also hope that the tank valve has the ability to shut off 100%.

Tom Endy

If the electric fuel pump is wired into the ignition circuit, how can it pump four gallons on gas into the intake if the car is turned off? Another reason for a battery switch.

[BILL WILLIAMSON]

Gravity flow can push fuel through a fuel pump & it must have had a funky needle/seat & slowly dribbled gas into the manifold & cylinders & leaked past the rings into the pan. Bill W.

[Juggler]

Originally Posted by john in illinois

I have a new English 97 on a heated Charley Yapp manifold. It runs noticeably smoother than the Zenith. Used an air/fuel meter to check jetting. smaller jets were too lean,stock jetting was just right.

It is a little touchy to start hot. I think I will try a heat insulator betweeen carb and manifold.

Air filter in pic is too restrictive. A 4" tall K&N works good.

I have the same setup

A phenolic spacer twixt carb and manifold fixed it

As you say, stock jets have worked for me.

[Tom Endy]

Originally Posted by denis4x4

If the electric fuel pump is wired into the ignition circuit, how can it pump four gallons on gas into the intake if the car is turned off? Another reason for a battery switch.

You cannot wire an electric fuel pump to the ignition circuit in a Model A with a stock ignition set up. If you do you will have the pump in series with the coil and parallel with the points and the engine won't run.

The fuel pump did not pump fuel into the engine because it was shut off. The fuel fed by gravity from the tank past the stationary fuel pump into the down draft carburetor then leaked past the float valve in the carburetor and into the intake manifold. From there it was all down hill into the engine.

An electrical shut off would not have anything to do with the situation. What was needed was for the owner to shut off the fuel valve under the tank and hope it had the ability to shut off 100%.

This type of leakage does not happen on a Model A equipped with the updraft carburetor Henry delivered with the car. The updraft carburetor sits below the manifold and valve ports. Fuel leaking past the float valve in the carburetor ends up on the garage floor not inside the engine.

Tom Endy

[denis4x4]

Tom, thank you for your explanation. Even though my Model A engines are not stock, i do use the stock fuel tank shut off on the '29 CCPU.

[John LaVoy]

The Weber works very well. We have it on the sedan and the roadster pickup. Tom's warning is correct for the shut off. Arizona Model A is a great source for the whole package to install the Weber. 480-782-0266 www.arizonamodela.com

[hotrodalley]

Holley 92

I am replacing my Weber with a Holley 92 on a vintage Burns Intake. The Weber is a good setup, but I just cant get used to the "modern" look. In addition, i am replacing the stock head with a hi compression Cyclone head. The engine is stock rabbit. Hope it all works. I know I will have some plumbing design to do for the fuel line and electric pump. I have an indented firewall so mounting a pump on the inside of the firewall is not an option. Holly 92's are a little difficult to find, but I have run them in tandem on a hopped up banger and they are great. I assume a single 92 on a pretty stock motor will be ok.

[john in illinois]

Originally Posted by Juggler

I have the same setup

A phenolic spacer twixt carb and manifold fixed it

As you say, stock jets have worked for me.

Thanks for the feedback,I will try it.

John