Testing and adjusting the Zenith 04 Carburetor on your Model T Ford
Last time we went through the cleaning / rebuilding process for the Zenith updraft 1″ bore 04 carburetor. Let’s see how this thing runs!
We pulled the choke wire and; with the key off, pulled the crank up 1/4 turn four times. With the throttle open a few notches and the spark lever all the way up we turned on the key. The crank was pulled up and the engine started on that first pull. All was not well. The engine was running quite lean. There were infrequent backfires through the carburetor, response was poor, and it would not idle. The mixture screw was adjusted for full rich and some improvement noted. But it was still very lean.
With the carburetor back on the car again we repeated our starting sequence. The engine again fired up on the first pull of the crank. It was noticeably improved. Gone was the backfiring through the intake. Engine acceleration now has no bog, it runs very well overall. Idle quality is the only thing that we think can be improved. We have (so far) only tried the two largest main and compensating jets. We think the combination of the smaller compensating jet with the larger main jet may prove to be the best combination. We don’t have time right now to try it, so it will be a future episode. More to come!