A combustion-powered nail gun including an arrangement for promoting a piston
returning
motion to its upper dead center. A combustion chamber frame is movable toward and
away from a head cover at which a spark plug is provided. When the combustion chamber
frame is in close contact with the head cover, a combustion chamber is provided
among the combustion chamber frame, the head cover, a part of a cylinder and a
piston. After the piston reaches the lower dead center as a result of combustion,
a thermal vacuum is provided in the combustion chamber for allowing the piston
to move toward the upper dead center. The combustion chamber frame has a through-hole,
and a valve is provided for normally closing the through-hole. A solenoid is provided
to selectively open the valve for leaking an increased pressure in the combustion
chamber through the through-hole during the return stroke of the piston.
