A fuel system is provided for a combustion-powered tool (10) having a self-contained internal combustion power source (16) with a combustion chamber (62), and constructed and arranged for driving a drive blade (88) to impact a fastener (N) and drive it into a workpiece. The tool (10) includes a housing (12) having a main chamber (14) enclosing the power source (16) and having a first end (28) adjacent a nosepiece (76) wherein the fasteners (N) are positioned prior to driving, and a second end (34) opposite the first end (28) and adjacent the combustion chamber (62). A fuel cell chamber (18) is in communication with the main chamber (14) and has a first chamber end (28) corresponding to the first end (28) of the main chamber (14) and a second chamber end (40) corresponding to the second end (34) of the main chamber (14). A fuel metering valve (44) is disposed in the fuel cell chamber (18) at the first end (38) so that a fuel cell (50) having a fuel outlet end (52) operationally inserted into the fuel cell chamber (18) will engage the valve (44) so that fuel is dispensed into the valve in a location closer to the first chamber end (38) than to the second chamber end (40).