Series 3 and 4 carburetors are generally used on 8 through
12.5 horsepower 4-cycle engines. The venturi size of these
carburetors are larger than Series 1 and Dual System
Carburetors. The quickest way to identify these carburetors
is by the presence of bosses on each side of the idle
mixture screw. To identify the Series 3 from a Series 4,
view the carburetor from the throttle end. The Series 3 has
(1) screw securing the throttle plate and the Series 4 uses
(2) screws.
