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

Carb bowl, float and bowl nut heavily coated with residue after months or years of storage with fuel in the tank (#1). Over time fuel breaks down and evaporates leaving behind residues that clog and gum up the float and fuel passages.

A closer view of the bowl nut (#2) that holds the bowl in place.

The bowl nut on this type of carburetor has holes in it to allow fuel to flow from the bowl to the main nozzle and low-speed circuit (#3). Blockage of these holes is the most common cause of trouble with this type of carb. Note the small hole just below the threads. This hole will supply the idle circuit.

#4 shows the small hole in the center of the bowl nut which feeds the main nozzle.

The step in the carb bowl should be aligned parallel to the float hinge rod when assembled (see #5 and #6). The small dimple in the deeper side of the bowl is there to help prevent the float from sticking to the bottom of the bowl.

With the bowl removed the float, bowl gasket, hinge rod and main nozzle within the center pedestal are visible (#6). Slide the hinge rod out either side to remove the float with the needle and clip.

The inlet needle is attached to the float with a spring clip (#7). When assembled, the straight end of the clip should point toward the air intake side of the carb. Check the float for leaks by shaking it. If you hear liquid sloshing around inside it, replace it. The float may also become crushed by water in the bowl freezing in cold weather.

This carb uses a replaceable rubber seat for the inlet needle (#8). The seat is inserted with the grooved side facing inward. Any debris or wear on the needle or seat will cause a poor seal resulting in a high fuel level in the bowl. This may lead to a rich running condition, flooding, or after a time the crankcase can fill with fuel. If your oil level seems high and/or is thin and smells like gas, you probably have a bad float, needle or seat.

A gray or black plastic restrictor cap covers the non-adjustable (fixed) low-speed jet (#9).

The brass low-speed jet is threaded into position (#10). An aluminum Welch plug to the left of the primer bulb covers the low-speed progression holes which can be seen in #17.

The low-speed jet has a tiny hole in its end that meets the side holes as demonstrated by a wire (#11).

When blowing out holes and passages with compressed air be careful not to blow too hard into the hole highlighted here (#12) or you may inflate and blow up the primer bulb.

A ball plug is installed during manufacture to seal where a hole was drilled into the center of the pedestal (center leg) (#13).

#14 shows a cutaway view of the hole opposite the ball plug in the previous photo. Fuel for the low-speed circuit comes through the bowl nut side hole, through this hole, continues past the Welch plug in #10 and on to the progression holes in #17. When this hole is clogged the engine might not run at low speed and may surge at high speed. Shooting carb cleaner into the hole from which the low-speed jet was removed should result in a stream squirting out this hole.

The main nozzle can be pressed out from inside the carb throat with the flat blade of a screwdriver, but it is seldom necessary to remove it (#15). If it is removed, one O-ring will likely remain in the carb body and will need to be fished out.

The main nozzle O-rings are 1/4 O.D. and 1/8 I.D. (#16).

The throttle plate has a coined edge which faces outward (#17). The scribe mark also faces outward and is in the 12 o'clock position on 2-7 HP engines. For 8-17 HP engines the mark aligns to the 3 o'clock position. Also seen here are the four progression holes which supply fuel near closed throttle position.

#18 shows the position of the throttle return (torsion) spring.