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Small Engine Repairs and Troubleshooting

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Briggs Carb 790120 - Carb with bowl removed

Disassembly of 790120 Carb used on Briggs and Stratton 128600 Series Engines (128602 0304)

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Photo - Briggs Carb 790120 - Carb with bowl removed^ Photo 1. Carb with bowl removed

Remove bowl nut and bowl (Photo 1). If the bowl doesn't separate easily, it's just stuck on the bowl gasket.

The bowl nut on this carb has a small fuel passage in the center (Photo 2) that connects to the hole in the side (Photo 3). These holes must be clean and are the most likely source of any problem with the carb.

Photo - Briggs Carb 790120 - View of bowl nut showing center hole^ Photo 2. View of bowl nut showing center hole
Photo - Briggs Carb 790120 - View of bowl nut showing side hole^ Photo 3. View of bowl nut showing side hole

View of the side fuel passage hole in the bowl nut (Photo 3). Not shown is the bowl nut gasket which goes between the bowl nut and the bowl.

When the carb is held upside-down the float should rest parallel to the carb body (Photo 4) maintaining the fuel level inside the carb bowl. If it isn't parallel, replace the float, needle, and/or seat.

Photo - Briggs Carb 790120 - Float should rest level^ Photo 4. Float should rest level
Photo - Briggs Carb 790120 - Remove float hinge pin^ Photo 5. Remove float hinge pin

The float hinge pin slides out to the side (Photo 5). The float and float needle can then be lifted out.

Photo 6 shows a view of the float with its needle in position. Check the float for leaks by shaking it next to your ear, listening for fuel sloshing inside it. Check the needle for corrosion or wear.

Photo - Briggs Carb 790120 - View of float and needle assembly^ Photo 6. View of float and needle assembly
Photo - Briggs Carb 790120 - Carb body with float and gasket removed^ Photo 7. Carb body with float and gasket removed

This carb uses a replaceable rubber seat, visible in red in Photo 7. A new seat is installed with the grooved side in first, away from view. The needle mates with the chamfered hole of the seat, which faces outward.

Also visible in Photo 7 is the emulsion tube (brass) within the carb's center pedestal. This tube must be clear as it is the main path for fuel to enter the venturi area. The tip of this tube is visible sticking up in the center of in the carburetor throat in Photo 8.

Photo 8 shows a vent hole on the carb intake side which might be clogged in a very dirty carb (as due to an improperly installed air cleaner).

Photo - Briggs Carb 790120 - Vent hole in carb intake^ Photo 8. Vent hole in carb intake

Previous: Disassembling the carb from the engine

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