Rebuilding Tool List (Zenith 28/228)
Model identification (Zenith 28 & 228)
Main Metering System (Zenith 28/228)
Accelerating system (Zenith 28/228)
Do I have a 28 or 228 series carb?
The 28AV and BV, and 228-series carburetors are of the single barrel, downdraft type with a primary and secondary venturi. The secondary venturi is pressed into the primary venturi. Theese carburetors are of the “balanced” design in that all air for fuel bowl ventilation and idling must enter through the air cleaner. For this reason any restriction in the air cleaner will have a minimum effect upon the fuel-air mixture ratio. These models include single idle, main, accelerating, and power jets. The accelerator pump is operated mechanically by throttle movement through a link connected to the throttle lever. The power jet is operated by engine manifold vacuum.
The basic difference between the 28 and 228 series is in the idle system. The 28 series has a single idle discharge plug in line with the closed throttle plate. The idle needle valve is located in the air intake body.
Example of 28 series idle system
The 228 series includes a two hole idle system with one hole located above the closed throttle plate and the other below the plate with the idle needle valve located in the throttle body.
Example of 228 series idle system