The first digit of the D.O.M. Is last number of the year/decade it was made. the next three numbers equate to the numeric day of the year, like a Julian calendar. I would have to say your engine was made on the 114th day of 1991 or 2001, Tecumseh changed over to 5 digit codes in 2004 and I'm pretty sure this style wasn't around in 1981.