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.
02 - Clogged fuel filter
As fuel is consumed, the level in the fuel tank lowers. To make up for this, fuel caps will have a small vent hole or holes to allow air into the tank. If the vent holes are blocked by buildup or debris, air will not be able to enter the tank, creating a vacuum that can cause the engine to stall. Try loosening the cap slightly then start the engine, if the engine continues to run normally, it is likely the vent hole or holes in the cap are blocked and the cap will need to be replaced.