This may be a silly question but here goes:

I'm fairly used to 2-stroke engines and am finallly getting into using 4-strokers.
Got my first recently, a Magnum XLS 52 and want to do a good break in.

Manual recommends fuel with 10% nitro and at least 20% castor oil. Best I could find at the
LHS was a 10% nitro with castor/synthetic blend fuel. I bought some castor oil from the LHS
as well and was intending on adding some castor to the fuel. Question I have is how much
castor to add for a gallon of fuel of this type that won't impede engine performance.

Thanks for any opinions!