> What plugs should be used in 1991 Max.  

The best are probably NGK DPR8EA9 or Autolite 4153.

> What gap ?  Bike 100% stock.

.035 in (.9 mm). Also note you will need an 18mm deep-well socket, 
standard-size spark plug sockets will NOT work.

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NGK DPR8EA-9 are the standard stock plug.
NGK DPR8EVX-9 are the platinum ones.
I use platinum and they work great.  Been in the bike for two years.

Jean(John),VMOA#425