Mr. Cuda:
You are getting some very conflicting advice here. I don't claim to be an expert, but my experience with rebuilding Zenith carburetors has taught me that three very important factors have to be achieved if you expect to have a properly functioning Zenith.
1. The passage ways must be open.
2. The jets must be flow tested and resized to the original spec. Most repos and many originals have been molested over the years are way off the mark. For instance, if the comp jet flows more than the cap jet the GAV circuit is useless.
3. The float valve must be properly set, and it should be able to hold the set level for a reasonable amount of time.
To return to your original question and your photo, the float valve on the left is a repo of the original type. It has a steel needle valve inside. The one on the left is also a repo known as a gross ball valve. it has a small ball and a large ball inside. I have seen a number of these fail. It may have something to do with the gas here in California. What happens is the small ball sticks in the seat, probably because there is not enough weight to dislodge it from the goo in the gas.
You can get a viton tip valve from Bratton for about $10. I have had very good luck with these. It is important that the valve not only shuts off at the proper set level, but holds that level for a reasonable time. The viton tip valve seems to do that well.
Go to
www.ocmafc.com It is the web site of the Orange County Model A Ford Club. On the menu at left scroll to "tech articles" and click. It will bring up a new menu. At the top is my name, click on it. It will bring up a menu of tech articles I have written. Scroll down to the bottom. There is two Zenith articles listed. One is the one another barner in this string mentioned. Click on these. You can down load them, print them out, and use them as you see fit. There is a photo of a flow tester, a float lever setting jig, and a photo of a Bratton viton tip float valve.
Flow testers are not hard to build. There are several people in my club who have constructed one. The fountain pump is so you can recycle the water and work indoors without flooding the place. Flow testing and resizing jets is a time consuming tedious job, but it is very important if you want to have a good functioning Zenith.
Good luck with your project.
Tom Endy