It is not unusual for riders to want to ensure they have maximized the amount of fuel they put into their motorcycle's gas tank. However, it is generally not recommended to attempt to squeeze the pump for extra gas once the gas pump has stopped.
Modern gas pumps are designed with safety features that automatically shut off the flow of fuel once the tank is full. This mechanism helps prevent overfilling and potential spills, which can be hazardous. Attempting to force extra fuel into the tank by squeezing the pump can lead to fuel overflow or other safety issues.
Additionally, motorcycles, including Harley-Davidson Sportsters, have a venting system in their gas tanks to allow proper airflow and prevent pressure build-up. Overfilling the tank by forcing extra gas into it can disrupt this venting system and potentially cause fuel leakage or other problems.
It's best to follow the instructions provided at the gas pump and rely on the automatic shut-off feature to ensure a safe and proper fueling process. If you find that your motorcycle's gas tank is consistently not holding as much fuel as you expect, it may be worth having it inspected by a professional to rule out any potential issues or concerns.