straight 30 or a 10w30
Briggs and Stratton only recommend using their own brand of lawnmower oil. This oil is available in stores for around $6 for 18oz. This particular oil is designed to be compatible with air cooled engines.
what grade of oil on this engine
your rings are most likely bad
SAE 30 weight.
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.
SAE 10w30 full synthetic and change it once a year.
Briggs and Stratton recommends SEA30 oil.
sae30
5w30
5w-30..or any 30 w oil will work..takes about a half a quart no more!
In moderate temperatures, as in a lawnmower used in summer, most will use straight 30W oil.
My 6.75hp Briggs calls for 30wt, so I would make a reasonable assumption that the 6.5hp calls for the same.