Zenith 28/228 Identification
Zenith 228

Zenith put a round aluminum tag on most carburetors located on the top of the carburetor. The number is stamped on the round tag. Buy your Zenith 28/228 carburetor parts here.
Zenith 28 228 Series Identification, Parts List, Exploded View
I have a 59 GMC pickup that has a 270ci with a Zenith 28/228 (228BV11) carb on it. I seem to have air screw holes on both the carb and the throttle body. The throttle body had a screw in it when I got it, and the hole on the carb was wide open. I watched your videos on youtube and you mention that a 28 should have the screw on the carb and the 228 should have it on the throttle body. What do I need to do to correct this?
Assuming someone hasn’t put a 28 top on a 228 bottom, you simply plug the top hole. Use a carburetor clean out plug and if you don’t have one of those, use a small amount of JB Weld.