Abstract: A carburetor comprises: a main barrel; a throttle situated in the barrel; an idle system which, from a cavity full of fuel, opens into the main barrel through progression and idle mixture holes; the idle system comprises elements for metering fuel and air, which form a primary emulsion. There are several suitably sized passages in the idle system through which the fuel or emulsion flow; the following cooperate with the said passages: first elements for excluding the flow from some of the said passages, keeping at least one open to prevent the idle system from emptying during accelerator release; second organs for positioning the said first elements; third devices for recognizing accelerator release and checking the said second organs.