Using To Much Thin Oil In Gen Set Is Not Recommended Since Its Air Cooled And Will Consume Oil And Run Hotter.....Thin Oil Will Burn More And Leaks More Evenly Than Thick....So It Will Leak From Seals More...And Everywhere When Your Gen Gets Bit Older....
20w-50 Will Normally Do Best ...Just Do Oil change On Time...And Tappets Need To Be Adjusted On these OHV Engines On Yearly Basis..Or Quarterly Or Half Yearly Depending On Use