with continuing attention to the drawings wherein applied reference numerals indicate parts similarly hereinafter identified the reference numeral 1 indicates generally a carburetor having a compartmented fuel bowl at 2 within which is disposed a mixing valve indicated generally at 3 the fuel bowl is served by a main fuel line 4 with a float at 5 regulating the flow of a primary fuel such as gasoline into the fuel bowl an auxiliary fluid flow to the carburetor is via a source shown as a conduit 6 which delivers the auxiliary flow via an inlet controlled by a float 7 a three way valve 8 normally directs an auxiliary fluid flow to mixing valve 3 via conduits 9a 9b both conduits 4 and 6 are served by upstream pump means such as conventional fuel pumps actuation of three way valve 8 from its position shown is by a solenoid 12 which valve then serves to route only a flow of the primary fuel into conduit 9b from a fuel outlet conduit 10 a switch 11 closes after engine starting and warm up to terminate the flow of the primary fuel through conduits 10 and 9b after engine starting and an initial drive away period switch 11 may be heat or timer actuated an air horn is indicated at h within which is a choke valve 13 actuated by an.