A combustion nailer is configured for use with a fuel cell having an internal metering valve and a reciprocating, biased main stem. The nailer includes a tool housing defining a fuel cell chamber constructed and arranged for receiving the fuel cell, a fuel cell actuator assembly configured for actuating the fuel cell in the chamber to emit a measured dose of fuel during tool operation, and a fuel delivery apparatus associated with the actuator assembly for receiving the emitted dose of fuel and providing it to a combustion chamber. The fuel delivery apparatus is configured for preventing actuation of the main stem by the actuator assembly upon the fuel cell being adapter-free.