Hi again, Steve. I think you will find that the last 2 digits of the Code are 20 - the engine seems to have been made at Briggs' flagship plant at Wauwatosa, Wisconsin, where their head office is located.

Your engine is an Intek. Here is the Illustrated Parts List:
http://bsintek.basco.com/BriggsDocumentDisplay/18hnxKXAnfBhU7y.pdf

Here is the Operator's Manual:
http://bsintek.basco.com/BriggsDocumentDisplay/flmmwKX-nfBhU7y.pdf
If you refer to Page 11, you will see the required maintenance schedule - tappet adjustment is the last item shown, required once per year.

Here is the section of the workshop manual that deals with adjusting the tappet clearance:
[Linked Image]

Here are the required clearances:
[Linked Image]

The Intek is an unlovable engine in my opinion, but with careful maintenance as prescribed it can give good service, though it may require occasional repairs.

The engine has a decompressor, as nearly all OHV mower engines do, because the compression ratio is fairly high, unlike the side valve engines which used to be popular years ago. The high compression ratio results in substantial fuel savings and higher power output, but it makes the engine far more difficult to crank than a side valve engine. The size of starter motor, associated wiring, and battery that would be required to crank the engine at full compression is considered impractical by the engine manufacturers, so a decompressor is used. It bumps the exhaust valve open momentarily about half way through the compression stroke. When the engine starts, the decompressor disengages automatically - it only operates at engine speeds below 600 rpm, which is less than half of the engine's idle speed.