The residue that results from old fuel being left in the tank can create a restriction in the carburetor. This is why you should always use fresh fuel when filling the tank and a fuel stabilizer to help maintain the quality of the fuel. You can try cleaning the carburetor with carburetor cleaner to eliminate the clog. If cleaning is not effective, you can often purchase a carburetor repair kit to replace some of the components or install a new carburetor altogether.
As fuel is consumed, the level in the fuel tank lowers. To make up for this, the fuel caps have small vent holes to allow air into the tank. If the vent holes are blocked by build-up or debris, air will not be able to enter the tank, creating a vacuum that will cause the engine to stall. You can replace the fuel cap with a new one to solve the problem.
03 - Defective spark plug
Due to carbon buildup and a weakened electrode, the spark plug will degrade over time which can cause the engine to stall. You should inspect the spark plug for damage or wear and you can also use an ignition tester to help determine if the spark plug is defective. Generally, we recommend replacing the spark plug with a new one once a year.