There is a flow chart. It was put out some years ago by Double D Productions. These were the folks in the Dallas MAFCA club that put out a very excellent video on Zenith restoration. The video is called Carburetors and Carbohydates. It is a color video on VHS or DVD. Bratton's carry it under part numbers 37990, 37991, $39.95.
Our club bought a copy years ago. It came with a chart that specified drill sizes for the jets. The problem is that drilling is not accurate. You can drill half a dozen jets out to the same size and they will all flow at different rates.
The flow chart I use I believe was specified in the video. I cannot attest to its authenticity or if it was sanctioned by Henry, but I have been using it for years and it seems to work.
Main - 140-150
Cap - 150-185
Comp - 138 - 142
Idle - 44 - 48
The values are in CC's per minute.
When I flow test I have a valve I turn on to allow water to run through the jet. It has to flow in the direction that fuel would flow in the carburetor. I time it for one minute while capturing the water in a chemistry lab beaker with CC graduations on it. It is a time consuming and frustrating procedure. You may end up flow testing, re-soldering and drilling the same jet out three or four times.
The best way to go about it is to have a seminar with three or four guys and set up an assembly line. One guys does the testing, another does the soldering, another does the drilling. You can spend the whole day at it. The trick is to do them as sets, mark the flow rates on a card and put the card and the jets in a plastic envelope. Then when you rebuild a Zenith all you have to do is reach for one of the plastic envelopes.
My process is to drill the jets out to about two sizes smaller than what is specified in the drill chart, then flow test it. It should flow test low. By running the same drill bit back through it it usually makes it larger. The plan is to sneak up on the flow rate.
Tom Endy
