You have a 1979, Yamaha built (for Merc) Mariner.
It is a carbon copy of the 1972 thru 1978 Yamaha model P400, later called a Model 20A.
Your serial/model number is sometimes listed as 653-304660 OR 653 ML 304660 depending on the parts list/source.
The 653 is Yamaha designation which identifies it "mechanically" as a (Yamaha) P400/20A
M - manual start (rope start) from factory
L - long shaft (20" transom model)
304660 is the actual "serial" indicating 1979 production, so one year after Yami discontinued it as a Yamaha model
Merc called this a Mariner model 20A and no longer show parts lists for this particular model - you will still find Mariner 20C parts lists listed but you can not swap parts - they were very different motors.
You can use a Seloc's (manual number 1400) - "Mariner Outboards 1977-1989 1&2 cylinder" but you may have extreme difficulty finding even the most basic parts for this particular motor (unless you happen to be in Australia or Asia where this model was popular - not so much in North America).
