Lean-burn engines now being developed employ in-cylinder injection which requires high pressures and so necessitates expensive injection equipment.The injection system proposed here is an air assisted in-cylinder injection system which is injecting a mixture of air and fuel in the cylinder during the intake stroke and allowing atomization at lower injection pressures than those necessary in compressing fuel with a usual solid injection.This time, the experiments used a testing engine of a 4 stroke gasoline OHV type replacing the Side Valve type. Performance with a small depression in the main combustion chamber was investigated with a spark plug and reed valve installed in the depression. The engine was operated then following the same method as last year (SAE 982698).As a result, the lean burn method employed here was possible over a wide range of engine speeds and loads. Moreover, it was also shown that this operation was possible with a fully opened throttle valve. With this arrangement, a stable idling operation was possible to air-fuel ratios of 55. With a lean burn at light loads including idling, a 8∼25% improvement was confirmed with specific fuel consumption ratios. The exhaust emission with injection had lower CO and NOx concentrations but a slight increase in HC. Smoke concentration was a very small quantity of 2∼3% of Bosch smoke value.