Three generations of carburetors

[NealW]

One of the reasons that I enjoy being a caretaker of a Model T is the opportunity to learn about and experience using car technology from a different era. That experience was expanded for me this past summer when we picked up a 1929 Model A. Most Model T owners know that much of the mechanicals of the car didn't undergo major changes during its production run, the carburetors designed and built by the two suppliers (Kingston and Holley) underwent quite a few changes. Those changes were mostly to simplify the carburetor and reduce cost. The Model A had a shorter run of only 4 years and the carburetor used on the car, either from Zenith or Tillotson, remain largely unchanged. Zenith stopped producing Model A carburetors at some point in the 1930s, and the Marvel-Schebler company came out with their own version to sell to the aftermarket under the Allstate brand for Sears.

This past week I finished rebuilding one of the Marvel carburetors and took a picture of it next to a rebuilt Holley G Model T carburetor and rebuilt Zenith Model A carburetor (shown below). The Holley G is considered by many to be one of the best early Model T carburetors (and I happened to have one on hand), so it is shown for this comparison. The Zenith carburetor was a major improvement in carburetor technology over the Model T carburetors, and a bit more complicated. Even so, they are very easy to work on. They do have 4 jets to handle both idling and higher RPM/power conditions. They have a float and needle like a Model T carburetor and yes, they can overflow too if something gets under the needle! The Model A at least has a fuel shutoff under the dash which is much more convenient than having to crawl under a T or opening the hood of a T if the car has a shutoff installed at the carburetor. The diagonal cylinder on the two A carburetors is where the mixture and choke lever attach. On the bottom of the Zenith you can see a large head of a bolt. That is the single bolt that holds the two halves of the carb together. That was Henry's input to the design. It originally had multiple bolts and he told them to simplify it.

The Marvel carb is a little simpler than the Zenith, with only 2 jets. It is an "emulsion tube" carburetor with a more complicated main jet. The float hinge is oriented so that the float is sideways instead of facing forward in the Zenith design, and that supposedly helps prevent the sloshing in the bowl from a sudden start and stop. The Ford Model B Zenith carb's float was similarly arranged. The biggest drawback of the Marvel design is that it uses an aluminum body, which is easy to strip out the threads. I had to put a threaded insert in the inlet attach flange on this carb. I have not yet tried the Marvel carb on the Model A, but "according to the internet", a lot of Model A owners consider it the best carb for the Model A. You would hope so since it was designed in the 1930s when even more was known about carburetor design. I have seen an airflow test comparing the Marvel to the Model A carburetors and it definitely flowed more air at partial throttle settings than the stock carburetors. At full throttle, they were all about the same as you would expect with all having the same throat diameter.

Anyway, I thought others may enjoy seeing how the carburetor technology changed during the Model T and A era. If any of the forum owners have or are considering getting a Model A in the future, a great source for Model A carburetor parts is from Renner's corner (link shown below). Very nice parts for a reasonable price.

Neal

https://www.rennerscorner.com/index.html

[TMiller6]

My comments on the Zenith carburetor.

Harold Hicks at Ford was tasked with producing 40 horsepower out of the A Engine. He found the Zenith carburetor capable of this. Henry did encourage the designers to cut complexity to the point of having only one bolt secure the bowl. Tillotson was an aftermarket offering that was never offered on the Model A from Ford. Other manufacturers were enlisted to produce the Zenith so a -1 or -2 was added to the bowl to identify makers since the carbs were identical. The Zenith-3 is the carburetor on my ‘31 Ford. It has a different inlet with a side bowl strainer/ sediment bulb with a drain. And my fuel shut off is under the hood because Ford changed the firewall and relocated the gas shut off in 1931.

[NealW]

Tillotson was an aftermarket offering that was never offered on the Model A from Ford. Other manufacturers were enlisted to produce the Zenith so a -1 or -2 was added to the bowl to identify makers since the carbs were identical. The Zenith-3 is the carburetor on my ‘31 Ford. It has a different inlet with a side bowl strainer/ sediment bulb with a drain. And my fuel shut off is under the hood because Ford changed the firewall and relocated the gas shut off in 1931.

You are correct. My mistake on the Tillotson. Again, "according to the internet", it seems at least that some of the A owners don't care for the Tillotson carb. The Zenith on our A seems to work well, but it also has calibrated jets from Renners and other new parts.

I wonder why Ford moved the shutoff to the firewall. Seems like a step back from the convenience of being able to shut it off before getting out of the car.

[Norman Kling]

I had many Model A's before I got into T's. In fact I was one of the charter members of the Model A Ford of America which Walt Rosenthal helped us get started.
My first car was a January 1929 A. It had many of the features of the 28. Probably registered as first sold in 1929. When I got it it had a Tillotson Carburetor. One day while I was driving to high school, it started running rough and choking or adjusting the richness didn't help. Finally it quit altogether! When I opened the hood, I found that the threads were stripped and the carburetor was just hanging by the fuel line and choke and throttle levers! I put a Marvel Carb on it and it ran great. One of the things the club did was to have a test when the cars started out the fuel valve was turned off and whoever went the farthest won. The float bowl on the Marvel must have been bigger than the others, because I won the test! I put on a Zenith carb and from time to time the float would stick. I remember going to meet a friend and as I was going up the hill at night, the float stuck and the engine quit. I was rolling backward and couldn't see the road behind me and ran the back wheel off the road. So I walked home and my dad came down to help me pull the car out. That was when he ruined his clutch. I could tell you a lot more stories about A's but this is enough for now.
Norm