may flow from the fitting 258 into the chamber 256 and through the slot 292 for fuel enriching the air passing through the air horn 288 and the opening 276 with reference again to fig3 and 5 of the drawings as gas exits from the chamber 192 through the fitting 202 to the mixer assembly 64 a slight reduction in pressure is realized in the chamber 192 and hence in the chamber 194 via the small diameter port 380 and the diaphragm 170 is thus slightly upwardly displaced in turn resulting in slightly greater opening of the valve 190 to allow a greater amount of fuel to pass from the chamber 144 into the chamber 192 for subsequent discharge from the chamber 192 through the fitting 202 as the valve 190 is further opened the end of the tube 195 remote from the underside of the diaphragm 160 experiences a slight surge of pressure and this surge of pressure is transmitted back through the tube 195 to the diaphragm chamber beneath the diaphragm 160 and thus supplements the upward thrust of the springs 162 on the center of the diaphragm 160 and thereby causes the lever 166 to allow the valve member 128 to move more fully toward an open position the pressure balance line 236 extending from the fitting 204 to the chamber 238 inwardly of the air filter 240 automatically compensates for the air filter 140 becoming dirty and resisting the flow of induction air therethrough when the air filter 140 becomes dirty and resists the flow.