I was given an OBM without a cover. Made in 1971, motor type ?-642-02E, motor serial number 6531653, fly wheel says Tecumseh, a number on the fuel system is 373-2324, it is a single cylinder air-cooled, has a neutral-forward cluch, two knobs (choke and ?)and a speed lever. Can anyone tell me the Make, HP Rating, and the Model? (I was only told it could be a Sears OBM, 4-hp but they weren't sure.)