Cost reduction is an important development goal for small motorcycles (1). As a way to reduce costs, we have developed an electronically controlled fuel injection (hereafter FI) system without a throttle position sensor (hereafter TPS). Ordinarily, the high throttle range is controlled and computed by TPS, and the low throttle range by manifold pressure sensor (hereafter MPS). The intake airflow is estimated with consistent high precision regardless of the engine load, and the basic fuel injection is executed accordingly. Also, transient correction monitors the size of TPS changes, to inject fuel immediately when a TPS change equal to or greater than a threshold value is detected. In our development, we replaced these functions with control by MPS. For calculation of basic fuel injection quantity by MPS, we carried on the conventional method. However, MPS transient correction control had some aspects with poor tracking. Thus, we constructed a new form of transient correction control, securing the following points. To estimate changed intake airflow, we calculated the size of MPS value changes between the previous cycle and the current cycle in the crank intake stroke, securing precision.We distributed the locations for transient correction into three before the completion of the intake stroke, making it possible to supply the calculated transient correction values to the current intake stroke regardless of the throttle input or engine state.We subtracted the manifold pressure change due to engine speed fluctuation from the MPS change calculated at the transient correction execution positions, preventing unintended injection while lowering the threshold value for transient correction.As a result, by using MPS without TPS, we succeeded in securing good throttle response which is comparable to that of conventional FI systems.