A fuel supply and combustion chamber system for a portable power tool, such as, for example, a fastener-driving tool, wherein the fuel supply and combustion chamber system can utilize liquid or gaseous fuels. The fuel supply and combustion chamber system can comprise multiple combustion chambers for achieving predetermined combustion and power output characteristics. In addition, the fuel supply and combustion chamber system can utilize portioning valve structures for providing predetermined amounts of either a gaseous or liquid fuel into the portable power tool combustion chamber.