Outdoor Power Equipment, Small Engine, Lawn Mower Repairs, Troubleshooting and Safety

A rubber gasket seals the opposite end of the emulsion tube body (a.k.a. fuel transfer tube) and carb body (#1). Fuel for the low speed circuit passes up through the two smaller tubes (#1, blue) to the low speed jets in the carb body. Fuel for the main circuit passes up through the larger tubes (#1, yellow) and past the emulsion tubes.

#2 shows a cutaway view of a carb with a bottom-mounted anti-afterfire solenoid. The solenoid screws into the main jet housing with the fuel bowl between the two. When the solenoid, fuel bowl and main jet housing are assembled, the main jet (#2, blue) should face away from the float hinge.

The main jet housing slides into the emulsion tube body and is sealed with an o-ring (#3). The anti-afterfire solenoid's plunger or pintle is tapered and seats into the center hole of the main jet housing. When the engine is shut down the spark is disabled and the engine coasts to a stop. While the engine is coasting, fuel is still being drawn in from the carb, and the unburned fuel continues out to the hot muffler where it may explode loudly. The anti-afterfire solenoid stops fuel flow into the engine as soon as the keyswitch is turned off. The plunger or pintle is extended at rest and retracts when supplied with 12 volts.

At one end of the emulsion tube body two large passages are visible. At the other end four passages, two large and two small, are visible. There are two horizontal passages connecting each of the larger passages to the smaller ones. The outside ends of these passages are sealed with ball plugs (#4, red).

Fuel from the two smaller tubes of the emulsion tube body flows up through the low speed jets (#5, red) in the carburetor body.

Fuel for the main circuit passes up through the larger tubes of the emulsion tube body and past the emulsion tubes into passages in the carb body (#6, yellow) on its way to the nozzle body . Air from the nozzle body flows down inside the emulsion tubes (#6, blue), out the tubes' holes and mixes with the fuel flowing up inside the emulsion tube body.

A view of the choke or air intake end of the carb shows the choke plate and nozzle body (#7).

Remove two screws and the choke plate (#8). The choke shaft and seal can now be slid out. Loctite 222 is recommended when re-assembling the screws.

The main supply of fuel is discharged from the nozzles (#9, yellow) into the venturi at the nozzle body (#9, blue).

Air enters into the middle holes (#10, blue) of the nozzle body and passes down inside the emulsion tubes to mix with the main fuel rising up in the emulsion tube body. The main fuel supply mixed with air flows around the emulsion tubes (#10, green) into the nozzle body and exits into the venturi. Air enters the top holes (#10, red) of the nozzle body and mixes with the low speed fuel supply.

The choke stop prevents the choke from going beyond wide open (#10, pink). Air passages provide venting to the fuel bowl (#10, yellow).

The top cover plate (#11) covers passages for the low speed fuel and for venting the bowl.

Fuel from the low speed jets mixed with air from the nozzle body rises up through the carb body (#12, blue) and exits into the carb throat at the discharge ports (#12, red). Air enters the choke end of the carb (#12, yellow) to vent the fuel bowl.

Fuel mixed with air for low speed operation enters the intake airstream near the closed throttle position. The primary discharge port is the small hole (#13, yellow). As the throttle opens, progessively more fuel is delivered through the slotted port (#13, red).

The throttle plates open bottom outward. The scoops on the baffle (if included) are at the bottom and face outward from the carb (#14).

The throttle plates are chamfered for a good seal (#15). Mark their positions prior to removal. Loctite 222 is recommended on the screws when re-assembling.