During the transition from idling to partial load, a steady increase of the fuel amount in proportion to the increasing air volume should be achieved. Also a carburettor engine should accelerate smoothly from the idling speed.
The main jet system does not yet
function when only slightly above idling RPMs, because the flow speed of the air is not yet sufficient. For this reason, with the increasing opening of the throttle valve, three drillings (or an oblong slit) become free. They are connected with the idling channel above the idling-mixture adjustment screw. Fuel from the idling system is also sucked in. 01/11