A new idea for realizing lean burn combustion with the low pressure port injection technique in S.I. engines, the technique of TEFI (Twice Electronic Fuel Injection per cycle), is proposed. That is, the total amount of fuel needed for each cycle is divided into two parts and injected at different timings to adjust and optimize the air and fuel mixture strength distribution in the cylinder. As a result, the air and fuel mixture strengths both at the spark plug region and in the whole cylinder can be adjusted arbitrarily. Therefore a lot of problems present in the conventional stratified charge engines can be avoided. Through the lean combustion experiment on a 5 valves EFI S.I. engine using the swirl control valve “SCV” technique, the advantages of the TEFI are confirmed.