Abstract: An air filter in front of the intake opening of the carburetor has an elastic lower surface (20) with a bead (19) which is movable in the intake opening. The displacement is adjusted by means of a choke control (22) which at maximum deflection presses the whole bead into the intake opening.

Abstract: In an ignition system having at least one glow plug, the filament thereof is supplied with power from a generator by means of a switch device. The power is controlled whereby a constant glow temperature level is obtained, for example by means of a predetermined resistance in the filament. The arrangement is associated with a Wheatstone bridge which, during a short interval at the beginning of every heat current cycle, is switched on when generator power is not yet supplied to the glow plug. The balance of the Wheatstone bridge, which indicates whether the glow plug is too hot or too cold, is registered for the present cycle by means of a comparator in which the balance is converted into a logical signal to be the basis for an on/off regulation by the switch device in the heating circuit of the glow plug.