Joe Lapine, Danbury Competition, told me to use Honda 4 stroke
oil 10W-40. It has the high
zinc levels like Valvoline VR-1 and Joe Gibbs.
Tom Lucas, FE Specialties told me to use Joe Gibbs 15W-50. He specifically said not to use
synthetic because it can cause rear main leaks with FE seals.
Call the guy that built your engine if possible.
John