Oil for a Generator

[blueST]

Anybody know what type of oil I should use in my 3Kw generator. It has a 6.5hp 4 stroke engine, no idea what make. The generator is a 2nd hand Rolson one that they don't seem to sell anymore. I have no documentation with it. Would like to change the oil to try to keep it reliable.

[thinfourth2]

cheap as chips multi grade

[tr7v8]

Most agricultural engines run a mono grade typically either SAE 30 or 40. So either Machine mart or local lawnmower place.