Automatic choke
The carburetor in these photos has an automatic choke. After starting the engine, the choke is kept closed by a bond attached to the diaphragm membrane. Once the engine starts, the carburetor venturi suction gradually pulls a section of the membrane for a few seconds, opening the choke through the linkage. The suction force acts through a small crest on the surface of the tank, which is seen in the picture above. If this flange is blocked, the choke plate will remain closed, flooding the carburetor.
Punctured diaphragm
A perforated diaphragm has symptoms that include a lack of response when the mixing screw is rotated clockwise, and the motor also continues to operate even when the mixing screw is fully tightened in the direction of the Clock needles. The engine will run erratically, intermittently, and fail due to excess fuel, and black smoke may also occur. The diaphragm is normally spent and pierced in the circular section that pumps the fuel. You can search for holding holes against a bright light or the sun. The only solution is a spare part.
