What is the reason for no fuel coming out when unscrewing below the carburetor?

[StMolly]

Reasons for no fuel coming out when unscrewing below the carburetor are as follows: Excessively lean combustible mixture: The carburetor backfire phenomenon is caused by the combustion flame returning from the intake pipe to the carburetor after the spark plug ignites the mixture, which is attributed to an excessively lean combustible mixture. Carburetor backfire: The mixture becomes so lean that the combustion speed is too slow. The time from the start of mixture combustion to its completion extends until the beginning of the next cycle's intake stroke when the intake valve opens, igniting the mixture in the intake pipe and causing carburetor backfire. Intake valve malfunction: The intake valve is stuck in the open position and cannot close. Reasons for valve sticking include scoring of the valve guide, bending of the valve stem, or loosening of the valve seat, all of which prevent the intake valve from closing properly. The spark plug ignites the mixture, which then ignites the mixture in the intake pipe, leading to carburetor backfire, and the intake valve being stuck open, resulting in incomplete closure.