to a carburetor c for the engine e via a main fuel passage lm which is provided at an intermediate portion thereof with a known switch cock v having three control positions 34 on 34 34 off 34 and 34 reserve 34 the auxiliary fuel g such as gasoline is supplied from the auxiliary fuel tank ts to the carburetor c via an auxiliary fuel passage ls which is provided at an intermediate portion thereof with a measuring pump p of the present invention the switch cock v and measuring pump p are fastened to opposite sides of a lower surface of the main fuel tank tm via a support member m and a bracket b respectively the construction of the carburetor c and measuring pump p will be described in detail hereinafter the carburetor c comprises a carburetor body 1 having an intake passage 2 extended horizontally through an central portion thereof and a vessel 4 defining a float chamber 3 and joined to a lower portion of the intake passage 2 the intake passage 2 having a central venturi portion 2a is provided therein with a choke valve 5 on the upstream side right hand side in the drawing of the venturi portion 2a and a throttle valve 6 on the downstream side thereof a starting nozzle 7 a by pass port 8 a primary nozzle 9 and a secondary nozzle 10 are opened into such positions in the intake passage 2 that are slightly downstream of the.