There is carbon build up on the cylinder head but I have decided it is worth it and not too bad at 30%. Having said that I would not use castor in a modern well-made 2-stroke engines however I feel that the low tolerences and extra friction in the HT engines make it worth the carbon build up as I have just witnessed it out perform motul 800t factory line.
I have used mainly Motul 800t factory line oil, top of the line synthetic and I have played around with other oils but castor is the only oil which keeps the engine performance from dropping after a long sustained run and a hot engine. Rides which normally leave my engine uncomfortably hot and feeling dry and 'angry' have been fixed with the r30.
I was surprised that it has had such a positive effect so I thought I would share it with you all