Rong, the stamped series of B&S numbers should be in three groups, Model, Series and Code. Model tells you the engine size, design generation, whether crankshaft is vertical or horizontal, type of carburetor, whether it has ball main bearings, and the type of starter. The Series tells you nothing you can make much use of except you can use it to find the right owner manual and parts list. The Code tells you the day, month and year it was made, and which shift/production it came from. The Code consists of eight numbers. Without those we can't tell the production date. The first number is certainly not a 9, so at least one of the missing two may be ahead of that nine.
