Weber carb?

J

JayJay

Well-known member
So: 1930s block, 0.040” oversize, Jim Brierley 0.340” “C” touring cam, recent ring and valve job, 5.2 head (installed in a 1931 S/W Town Sedan, Mitchell O/D). Will I see a significant increase in performance by switching from standard Zenith carb to a Weber downdraft? Experience trumps speculation. Thanks.
 
I think with those modifications you would see a big improvement power. The Zenith really limits air flow into the motor.
 
I don't know if anyone has actually put a Zenith on a flow bench. It would be interesting to see the difference between an A and B carb. The A made max power at about 2250 rpm. It was pulling about 100 cfm which is what some people guesstimate was the max flow of the Zenith A carb. I guess Henry figured if you restricted the air you limited the RPM - and warranty claims. The Weber replacement flows around 240 cfm.
 
The Zenith will perform just as well at low rpm, up to about 1,200. After that running the Weber on the 32 mm throat will be pretty much the same as the Zenith. But it you jump on the accelerator and also open up the 34 mm throat there will be a big difference.

I am not sure how much you want to push your original block. If you have a balanced crankshaft and light pistons that will help. Also insert rods. I use a redline of 3,000 rpm on my Burtz block but it could probably go more. You may want to redline your engine to less, say 2,000. With the Mitchell OD that will be a fast cruising speed. The Weber really shines at the higher rpm. The Zenith chokes the engine at the higher rpm.

Buy a set of jets and experiment. I run a larger jet in the 34 mm throat. I experimented with idle jets and the idle mixture to get a good transition from idle. Although you can buy high flow float valves, the standard float valve works best on the Model A. I think the Weber 32-34 carburetor was used on the Datsun cars.

The inside manifold nuts are hard to get to. I made an offset wrench out of a 11/16 box end wrench, some square tubing, and a 1/2-inch drive. I can use that to torque the inside nuts with my torque wrench. I use 55 foot-pounds, but others use less. I will retorque when I retorque the head nuts.
 
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Beware fake Weber carbs

Sammy at Arizona Model A does the complete kit - genuine new carb and manifold, linkages etc as a bolt on

He also does a neat cast iron exhaust manifold to go with
 
Juggler said:
Beware fake Weber carbs

Sammy at Arizona Model A does the complete kit - genuine new carb and manifold, linkages etc as a bolt on

He also does a neat cast iron exhaust manifold to go with
Click to expand...

He is the BEST place to buy a Weber carby - bar none. I have one of his and 1 fake one. Chalk and cheese!
 
He used to have one but prefers to speak to his customers on the phone

Sammy Guthrie
Arizona Model A
(480) 782-0266
15838 S Gilbert Rd Chandler, AZ 85225
 
Best to visit him in person, actually. You will be amazed. One day's drive from Southern California. Just spend the night there. Plenty of nice places to stay in that area.
 

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Expect less gas mileage and range as with most performance improvements.you might need a fuel pump and a bigger radiator .
 
Like all performance upgrades, it depends on how you drive it. My car has a Weber. If I take the back roads and drive at 55 or less I get 20 mpg. But if I am on the highway at 65 to 70 mph it drops to about 16 mpg.
 
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