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

The Series 7 carburetor (#1) is an emissions grade carburetor used on medium frame vertical shaft overhead valve engines. The float bowl, float, and main nozzle are non-metallic, which eliminates the corrosion and varnishing problems associated with similar metallic parts. Common service areas of the carburetor are contained in the fuel bowl, which include the float, needle, seat and main nozzle emulsion tube. All of these parts can be serviced without removing the carburetor body from the engine.

The fuel bowl is held to the carb body by a retaining latch (#2) that snaps into place. Use a screwdriver to pry the retainer down and away from the bowl to release it.

A welch plug covers the idle fuel mixing well (#2, red) where fuel and air mix during slow speed operation.

To remove the float, take a needle nose pliers and grasp the cross piece (#3, green) between the center leg (#3, yellow) and the pivot point (#3, blue) on the float. It is critical to pull the float straight out so as not to break it.

The float needle, or inlet needle, attaches to the float as shown (#4).

Fuel enters the bowl via the inlet tube (#5, green) as long as the float and needle allow. As the level of fuel in the bowl rises, the float pushes the inlet needle against the rubber seat, stopping the flow of fuel. Some bowls may also contain a clip or retaining ring, used to hold the rubber seat (#5, blue) in place. When replacing the seat, the grooved side of the seat goes in first, the side with the chamfered hole facing out. To install the float, place the float hinge pin into the hinge slot on the float and press into place in the bowl (#5, yellow).

All fuel in the bowl passes through the main jet (#6, red) which is held in place by a spring and the bowl drain screw (#6, yellow). Idle fuel rises up the center leg to the idle fuel jet (#6, pink).

Bowl drain screw (#7, blue), gasket, spring, main jet (#7, yellow) and o-ring (#7).

Some carbs may have an anti-afterfire solenoid (#8, yellow) instead of the bowl drain screw. 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 by a spring and retracts when supplied with 12 volts DC.

The plunger, spring and main jet can be seen in position at the bottom of the bowl (#8, blue).

Solenoid, gasket, spring, main jet and o-ring (#9).

The main flow of fuel, having come through the main jet, rises up in the emulsion tube where air from the main air bleed enters through holes (#10, green) along the side of the emulsion tube and is discharged into the intake airstream via the main nozzle (#10, pink) which extends into the venturi. An o-ring (#10, yellow) is used at the bottom of the emulsion tube; a spring below the tube pushes it up against the bowl gasket.

Alignment holes (#11, pink) in the carb body and gasket allow the bowl to be attached only one way. The main nozzle extends through the center hole (#11, yellow), up into the venturi. Fuel from the idle jet passes up into the carb body via the hole at #11, blue on the way to the idle fuel mixing well (#11, purple). Air from the main air bleed travels down through the hole at #11, white and mixes with fuel rising in the emulsion tube. The bowl is vented via the 2 holes at (#11, green).

During low speed operation, fuel from the idle jet and air from the idle air bleed (#12, blue) mix in the idle fuel mixing well and the mixture is discharged into the intake airstream via the primary idle fuel discharge hole (#12, green). As the throttle opens, additional fuel/air mixture is delivered via the progression holes (#12, red) .

When installing the throttle plate (#13) on the 2 - 7 hp carburetor, position the plate with scribe mark facing out and in the 12 o'clock position; 8 - 17 hp carburetor => 3 o'clock position. Make sure that the throttle plate does not bind.

Mark the choke plate before removal to indicate which way to reinstall it. With the choke removed, you can see the main air bleed (#14, pink). The bowl vent originates at #14, blue. The main nozzle (#14, green) extends into the airstream at the venturi. Choke stop (#14, yellow).

The idle speed screw (#15) limits how far toward closed the throttle may travel.

Choke spring assembly (#16).