between the float chamber 14 and the inlet port 38 of the fuel tube 26 and such flow will be unlikely to be disturbed and more especially in the case of a relatively high flow velocity through a small cross section will make a substantial contribution to avoiding the formation of vapor bubbles even under very unfavorable conditions the working example of the carburetor of the present invention described above leads to the advantages described initially herein a more significant point in this respect is that the relatively high pressure at the plane a makes it possible for the critical pressure ratio to be maintained far into the partial load range so that consequently more regular operation of the idling system may be ensured since furthermore in the partial load range as well a corresponding flow is maintained through the idling system and such flow may certain constitute a substantial part of the fuel air mixture made available for the cylinders the optimum operation at any rate of this part leads to a significant increase in mileage and a drop in contaminant emission in the partial load ranges as well for achieving a maximum vacuum in the idling setting the throttle valve 8 can be fully closed in this position with the possible exception of small gaps caused by manufacturing tolerances this position of the throttle valve 8 in the idling setting does also.