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

The Large One-piece Flo-jet Carburetor shown here is similar to the Small One-piece Flo-jet carb. Besides size, the difference is that the main fuel mixture needle valve on the Large model is below the float bowl.

The low idle needle (#2, white) meters fuel entering the carb throat while the throttle is near closed position (#5). The initial setting for the needle is 1-1/2 turns out (counter-clockwise) from lightly seated.

The idle circuit emulsion tube (#2, black, see also #6) brings fuel up from the main nozzle.

A ball plug seals the hole where the idle air bleed / idle progression hole was drilled (#2, yellow). The air bleed can be seen just prior to the idle fuel orifice (#5, white).

A ball plug (#3, yellow) )seals the hole where a connection was drilled from the idle mixture screw (#2, white), to the air bleed / progression hole (#5, white) and then to the emulsion tube (#6).

The idle fuel mixture adjusting screw (needle) and spring (#4).

The idle fuel discharge port (#5, black) and progression hole (#5, white) viewed from the engine side of the throttle plate. When the throttle is closed beyond the progression hole, the idle discharge port is exposed to high engine vacuum and the progression hole is exposed to atmospheric pressure, thus air will flow into the progression hole and mix with the fuel exiting the idle fuel port. In this case the progression hole acts as an air bleed. As the throttle opens, the idle fuel discharge port and the progression hole become are both exposed to engine vacuum and fuel / air mix is pulled from the emulsion tube and into the engine air intake stream.

The idle circuit emulsion tube (#6) has a number of air bleed holes along its length. Air enters the side holes and mixes with the fuel being drawn up the center of the tube and the fuel/air mix continues on to the idle fuel mixture adjusting needle (#2, white) and the idle fuel discharge port (#5, black) and idle fuel progression hole (#5, white).

On the large one-piece flo-jet carburetor, the main fuel adjusting needle is located under the float bowl (#7).

The bowl nut and main needle (#8). When installing the main needle, screw in and tighten the bowl nut first, then screw in the needle, spring, washer and o-ring, so as not to jam the needle into the seat.

Exploded view of the bowl nut and main fuel adjusting needle parts (#9).

With the carb inverted, the float should be parallel to carb body (#10). If it isn't parallel, the float can be adjusted by bending the tab where the float contacts the inlet needle.

Remove hinge rod by sliding it out (#11). The float can now be lifted away with the inlet needle (float needle) attached to it by a clip.

The long end of the clip should point toward the air intake end of the carb (#12). The inlet needle has a viton rubber tip to provide a good seal. Inspect the tip for signs of wear or a groove worn into the rubber.

The nozzle unscrews from the center leg (#13).

With float removed the inlet seat and bowl vent baffle are visible (#14). The seat can be pulled with a screw extractor or by tapping it and threading in screw and pulling it out.

Behind the baffle is the bowl vent passage (#15). (It is almost certainly never necessary to remove this baffle. It was removed here for demonstration purposes.)

The bowl vent passage connects to a hole in the air intake (#16, white). The yellow square shows the crankcase breather opening. The black square is the main nozzle vent or air bleed.

The crankcase breather tube connects to the carb air intake boss (#17).

A spring and washer hold the choke lever where it is put (#18). Clockwise closes the choke plate (choke on).

An exploded view of the choke detent parts (#19).

When installing the choke plate, position the choke shaft with the threaded holes down. Slide the choke plate into the choke shaft so the bump side of the dimple on the choke plate is downward (#20).

The idle speed adjusting screw determines how far the throttle may close thereby setting idle speed (#21). To remove the throttle shaft, drive or press out the roll pin that secures the throttle stop lever to the throttle shaft. When installing the throttle plate, position the throttle shaft with threaded holes up and slide the plate in with the bump side of the dimple downward.

The throttle seals are installed with the lips outward (#22).

To remove the throttle or choke plates and shafts and the venturi, the large welch plug at the air intake end of the carb must be pried or popped out from within the intake (#23). When installing a new plug, apply sealant to the perimeter, position the plug, flatten it somewhat with a couple of taps of a hammer, and stake or swage the perimeter in 8 places. (This carb originally was staked in two places).