Have you checked your fuel system for leaks lately? Turns out there's a good reason to periodically conduct a thorough investigation. Incipient leaks may go undetected. Worse, when the O-ring on the fuel-selector valve goes bad, it could allow air into the system, which means your engine could misbehave at a most inconvenient time. Often, this malady is difficult to diagnose and the assumption is that the fuel selector is OK when it is not.