Jinbei 49 1 Single-point injection engine started normally in the morning, driving for more than half an hour, and the idle speed increased when driving to neutral 1500 rpm or so-

Is the air intake system leaking (whether the rubber pipe connecting the air intake system is aging, whether the air intake pipe pad and throttle pad are leaking), or whether the gap of the throttle plate is too large (try to get a smaller one, or buy an old throttle plate from a scrap factory), whether the oil pressure regulating valve is still available, or whether your idle motor is really faulty, can you tell? Try another one.