Sorry, not trying to steer conversation away from generators, but this may be the same type engine?
The engine in my Vermeer stump cutter may be the same model 35 hp Briggs Vanguard.
These are Briggs & Stratton design, manufactured by Daihatsu (a subsidiary of Toyota) in Japan.
They get pretty hard workout in this service and I stick to 40 - 50 hour oil change.
This one has 870 hours on and so far never needed oil addition, however it gives slight puff of blue smoke when restarted while still hot after hard working!
To me that indicates it may be time to check & change the valve stem seals soon.
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