A gasoline engine boosting system including a fuel tank, an engine, a fuel tube, an accelerator line, a drive sprocket, a drive chain, a discharge pipe and a fixing bracket. The fixing bracket includes an adjustable engine fixing bracket. The adjustable engine fixing bracket includes a first front fixing rod, a second front fixing rod, a first rear fixing rod, a second rear fixing rod, a front fixing base, a rear fixing base, a first tube clip and a second tube clip, the front fixing base and the rear fixing base are respectively fixed on a front side and a rear side of the engine. The front fixing base includes a front sliding adjustment groove. The rear fixing base includes a rear sliding adjustment groove allow. The gasoline engine boosting system is adaptable to a bicycle frame.