Castor oil in model engines gives the 'tuning' a degree of lattitude if set up too lean...but this is generally only for the smaller 'glow' engines which operate at a lower temperature.

The other big difference in the oil quantity, or % in the fuel.
Glow engines take approx 20% oil as we all know, but petrol engines take a lot less. Also, the oil content required in petrol engines tends to vary between manufactures, due to internal design, and / or purpose.

I have an old 'chain-saw' converted engine which only needs 1-Part oil to 40 Part petrol, and does not seem fussy on different types. It has some lovely needle bearings on its con-ron.

Your Zenoah manual should advise on oil use, but you could use a little more to 'break it in'.

Its a popular engine maker, so you should get loads of advice from this column.

Just another thing....its interesting to note that petrol engines also have a considerably different air-fuel ratio!

...so the mixture is effectively leaner too!

Anyway, the Zenoah is a popular mfr. so you'l get loads of advice off this column.

Best of luck!