The Tecumseh Dual System Carburetor can be identified by its large derby-shaped primer bulb and lack of any adjustments. It is used on 4-cycle lawn mower engines.
The main feature of this carb is its lack of features. Externally, there are only a primer bulb on one side and a fuel inlet fitting on the other side (#2).
The float bowl (fuel bowl) is held by the bowl retaining nut (#3). The float bowl should be positioned so that the step in the bowl is parallel to the float hinge (#4).
After removal of the float bowl, the float, hinge rod and bowl gasket can be seen (#4).
The bowl nut has a hole in its side through which fuel flows to the nozzle (#5).
Fuel reaches the bowl nut through two holes in the center leg (#6).
With the carb inverted, the free end of the float should rest 11/64 inch from the body of the carb (#7). The float can be adjusted by bending the tab on which the carb sits.
The hinge rod slides out and the float can be removed with the inlet needle and clip (#8). Shake the float and listen to hear if fuel has leaked into it.
The inlet needle is attached to the float with a clip. The long open end of the clip should point toward the air intake end of the carb (#9).
The nozzle is made of brass and extends from the center of the venturi, down through the center leg, to the bowl nut (#10). The inlet seat (visible in green in #10) is made of rubber and is replaceable. It can be blown out with compressed air blown through the fuel inlet fitting, or fished out with a hook fashioned from a paperclip. It is installed with the grooved side inward and the smooth side with chamfered hole outward toward the needle.
#11 shows the air intake end of the carb.
At the six o'clock position is the nozzle vent (#12).
A wire shows the connection from the vent hole, just prior to the venturi, to the inside of the center leg (#13). This vent supplies air to atomize fuel rising through the nozzle.
The bowl is vented through the recess above a welch plug to the a hole in the carb throat prior to the venturi (#14).
With the welch plug removed, the vent hole (#15) can be seen which leads to the air intake area of the prior photo (#14).
The primer bulb is large and shaped like a derby hat (#16). It is held in place by the retainer shown.
Behind the primer is a hole (#17) that leads to the inside of the center leg, as shown by the wire in #18. Pressing the primer bulb forces air down the center leg, which forces fuel from the bowl nut up the nozzle.
The throttle shutter is installed with the scribe mark facing outward and in the 12 o'clock position (#19).