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.
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. I am using two matched 228 series in my GMC. Both style of carb are very similar. I can send along the Zenith service manual pdf if you would like. need a email address.
