A: Changing the Diaphragm:
These engines do not have a petrol pump. They have a DIAPHRAGM. When the diaphragm is ready to be replaced (typically after some 18 months’ use) it leaks air, and feeds petrol unevenly to the engine causing it to “hunt” (i.e. run unevenly in surges). This is accompanied by black smoke (excess petrol being burned off) and an increase in petrol consumption.
The diaphragm can be replaced by an authorised Briggs & Stratton dealer. This is a chargeable job and NOT a warranty repair.
If a user has a mechanical or practical nature they can buy the part from the dealer and fit it themselves. If doing this work oneself it is essential to:
• Work cleanly and ensure no dirt is introduced into the work, and
• Not stretch or distort the springs in the throttle mechanism behind the air
cleaner
The task has 4 separate stages:
1. Remove the carburettor and fuel tank.
2. Separate the carburettor and fuel tank.
3. Replace the diaphragm and gasket.
4. Re-assembly.
REMOVE THE CARBURETTOR AND FUEL TANK
1. Remove the carburettor and fuel tank assembly mounting bolts.
2. Slip the carburettor and fuel tank assembly off the end of the fuel intake tube.
3. Turn the fuel tank assembly to free the throttle link from throttle lever.
This stage provides a good opportunity to empty any sediment from the tank and to rinse it with petrol.
SEPARATE THE CARBURETTOR AND FUEL TANK
1. Remove the 5 screws securing the carburettor to the tank.
2. Remove the carburettor from the tank.
3. Remove the diaphragm and gasket from the tank.
REPLACE THE DIAPHRAGM AND GASKET
1. Place the new diaphragm on the tank top, then place the new gasket on top of the diaphragm. NOTE: It is worthwhile cleaning around the top of the tank with a clean cloth with some petrol on it to remove any grease or dirt so that an airtight seal is achieved with the diaphragm.
2. Lower the carburettor assembly down onto the gasket and diaphragm.
3. Replace the 5 screws and tighten them evenly.
RE-ASSEMBLY
Reassemble the tank assembly in the reverse manner to the disassembly described above.
Andrew Davey, March 2012
