At full load, the carburettor should enrich the, up to now, lean mixture in order to attain the performance promised by the manufacturer. The consumption and the exhaust gas values play only a minor role.
The vacuum generated by the through-flow of air is so strong that fuel is sucked in from almost all the openings. In addition to the main jet system, this can also be the idling- and/or the acceleration system. And indeed, it's possible that the enrichment is still not sufficient. An additional enrichment pipe with an exactly defined height, dips its nozzle into the fuel in the float chamber making a further enrichment possible.
At full load, the fuel is not only used to reach higher performance, but also (particularly in racing cars) for the internal cooling. 01/11