How to Replace Carburetor Diaphragms

Lawnmowers are powered by combustion engines that use carburetors.

Some two-cycle engine's carburetors operate with a diaphragm. The diaphragm is a rubber membrane on a carburetor that controls the needle valve, which in turn controls the fuel coming into the carburetor. Carburetors sometimes require adjustments and periodic maintenance. While there are complete rebuild kits available for carburetors, sometimes a diaphragm replacement is all that is needed. A diaphragm replacement project can be performed by someone with average mechanical skills with a few basic tools.

Things You'll Need

• Screwdriver
• Appropriate wrenches

Instructions

1. Remove the air filter using the screwdriver to loosen the screw that holds the air filter to the carburetor. Most air filters are secured with a flathead screw.

2. Remove the carburetor from the engine block using the appropriate wrenches to loosen the bolts that hold the carburetor to the block and control bracket. On some engines, the gas tank will be removed with the carburetor.

3. Separate the carburetor from the gas tank, removing the screws that hold the carburetor to the tank and unhooking all springs attached to carburetor. After removing the screws, slowly separate the carburetor from the tank. If the carburetor has an automatic choke, the cover will have to be removed using a wrench and the choke unhooked. At this point, the diaphragm should fall out.

4. Replace the old diaphragm with the appropriate diaphragm required by the engine model. If replacing diaphragm on an automatic choke carburetor, the choke spring must be attached to the diaphragm and reattached to the choke plate during this step.

5. Reattach the carburetor springs to former positions, place the fuel tank upside down on a bench and attach the carburetor to the tank tightening the screws one turn.

6. Hold the choke open past halfway using a screwdriver and gently move the carburetor to set choke spring. Tighten the screws to the tank in a staggered order.

7. Place the carburetor and fuel tank back on the engine in the reverse order that it was removed and replace the air filter, tightening the bolts and screws.

Tips & Warnings

• When disassembling the carburetor, lay the parts out in such an order to make putting the assembly back together easier.

• On automatic choke engines, when removing the carburetor and fuel tank check for fuel in the chamber that houses the long spring. If fuel is in that chamber the tank will have to be repaired with a repair kit or sent back to the dealer.

References

• Small-Engines: Briggs and Stratton Diaphragm Instructions

Resources

• Ereplacements: How to Clean a 2 Cycle Engine Carburetor