PURPOSE: To prevent an air-fuel ratio becoming too lean, which is due to the fact that a delay in air-fuel ratio judgment from 'lean' to 'rich' is over and the feed-back correction is forcibly controlled to the 'lean' side, under the condition that the air-fuel ratio shifts to the 'lean' side accompanying the start of supply of assist air.
CONSTITUTION: This invention is characteristic of an engine, which is provided with both an assist air supplying means and an air-fuel ratio feedback control means 33, being further provided with excessively-lean-air-fuel-ratio-preventing- means 37, 38 which function when the feedback correction is going to be made in the 'lean' direction and the time is in advance of the prescribed time 34, and moreover the assist air is being supplied.
SHIGENAKA YASUO
OKA KENJI
