Starting with the easiest possibilities...
Is it getting good unrestricted air flow through the cooling fins on the engine, are Any air baffles missing or blocked? It is after all an Air cooled engine. Grass can plug up & block air flow. Resulting in excess heat that will have a direct effect on fuel air mix as it heats... also excess heat will thin engine oils allowing leakage around seals...
What type and weight engine oil are you using? Run a good Multiviscosity Synthetic engine oil, it will deal with extreme heat and oil thinning... a Very good synthetic is Rotella T6, I run it in Every engine I have... :smile:KennyV