It was not easy to do. Getting a controlled explosion inside the combustion chamber required just the right amount of vaporized gasoline mixed with air. In the early days of motorcycles, engineers did not yet appreciate the details of fuel delivery and employed many different methods. Most utilized the suction provided by piston travel pulling air through an intake valve. None of the early carburetors could keep the air/fuel ratio (AFR) at about the ideal of 14:1 across the full range of engine RPMs (ie, idle to wide-open-throttle). For the Hendersons of the 1920s, the intake manifold was positioned so that fuel and air had to be drawn up from below and to do this, the Chicago factory abandoned the Schebler carburetor (used on the Detroit design) in exchange for a Zenith “updraft” model. By 1928, the Zenith T4X utilized several novel methods of controlling the AFR. Here is a diagram from Zenith, the supplier, back in the day:
Here is a photo of the T4X that came with my Deluxe:
When I first got my Deluxe running some years ago, I could not get it to run cleanly. It appeared that whatever adjustments I made to get it to idle correctly would cause it to not run properly when the throttle was opened way up. Eventually I took it apart to look at the metering jets (as shown as items I and G in the period diagram). Both were stamped with the number 20 – as they should have been – however a previous “mechanic” had opened one of the holes quite a bit larger. It also appeared that the shaft for the throttle butterfly valve was quite loose allowing for air leakage and sloppy control.
The short term solution was to borrow a working carb from my friend and fellow Cannonballer, Jeff. At the same time, Mark at 4th Coast Fours, was working on casting and manufacturing “new” throttle bodies, shafts and jets. As of this writing (days before the race start), I have not received one but I am told they have been test run successfully. It remains to be seen if I get one to mount in place the day before the race. Stay tuned….