Learn how to replace the diaphragm in a 3.5-4HP Briggs & Stratton carburetor with an auto-choke.
- Phillips Head Screwdriver
- Flat Head Screwdriver
- Socket Wrench - 13mm & 11mm Sockets
- Carburetor Diaphragm Kit
Remove the air filter by removing the screw which holds it in place. Once removed the auto-choke becomes visible, it may not function as well (may not spring back properly) if the diaphragm is in bad condition.
Using the socket wrench, remove the three bolts which hold the carburetor and fuel tank onto the engine. Pull the fuel tank and carburetor away from the engine gently, tilt forwards to disconnect the linkage to the throttle on the carburetor.
Remove the five screws fixing the carburetor to the fuel tank (there may also be a Phillips head screw underneath the choke, inside the carburetor, that needs undoing). Lift the carburetor away from the fuel tank, being careful not to lose the spring connected to the diaphragm (or the screw underneath the choke, if one was present).
Examine the mesh covering the ends of the tubes protruding from the bottom of the carburetor, they need to be clean and free of blockages. Undo the screw keeping the casing for the wire controlling the auto-choke in place. Unhook the wire, then gently remove the diaphragm from the underside of the carburetor (don’t lose the short spring and washer underneath the diaphragm, or the locking pin/screw).
Give everything a good clean. Then place the new diaphragm in position, ensure that you thread the wire controlling the auto-choke through the hole it was removed from. Clip the longer spring into place.
Turn the carburetor over, now that the diaphragm is in place, make sure you continue to hold everything in position. Line everything up with the fuel tank and sit the carburetor back on top of the fuel tank, do up the screws holding it in place. Don’t forget to reconnect the cover over the auto-choke wire. Reconnect the fuel tank and carburetor to the engine.