RE: Ben Buckle Elf
I am currrently running a saito 90 , OS 90 and a magnum 90 4 strokes all inverted and get no trouble on standard fuel -10% nitro and synthetic oil ( plus 2% castor) and never experienced any running problems ( ignorance is bliss ) plugs are either F or No 3
I do store models nose up to avoid oil pooling into plug. I keep the saito model inverted between flights as left too long - it will oil up
Engines have been well run in , but generally I have always installed inverted to suit model lines and have experienced only oiling up if left standing too long with engine in inverted postion. I believe oil burning off may well leave residue affecting plug and engine performance. If I do get an oily plug, I take out and wash with fuel
hope this helps
John