Lawnmower. It's a Briggs & Stratton engine.
what grade of oil on this engine
Briggs & Stratton
Briggs has a rudimentary wiring diagram for the operation of an electric start engine. see the link below.
The correct gap for the spark plug of a Briggs and Stratton 6.75 Lawnmower engine 0.030. Most new plugs come with that gap, but it is best to check to make sure.
SAE 30 weight.
why does my 4.75 BRIGGS & STRATTON lawnmower engine idles high and low when cutting my grass
It is 0.030" for an L-head engine.
Briggs and Stratton is a select brand of lawn mower. When oiling one's Briggs and Stratton lawn mower engine, it is best to use a high quality oil. One can find such an oil at their local home improvement store, such as Home Depot.
My 6.75hp Briggs calls for 30wt, so I would make a reasonable assumption that the 6.5hp calls for the same.
It is probably a Briggs & Stratton engine. You will need to supply the model number from the engine to get a correct gap.
Displacement and HP are only related to each other in a range because of engine variations. I agree but was curious how did you get the cc of a lawnmower? If it is a lawnmower the hp comes out with an educated guess of about 12 hp.