the blaster is notorious for having the air tube boot slip off the carb, check there for your air leak, it will cause it to over run even when key is turned off. the easiest way to stop it fast is slow it down pull in the clutch upshift to 6th and drop the clutch, it'll stall the motor if your slow enough don't forget to hold the brakes just in case. you could have blown the motor with out seizing it still though