I've used Optimol Opti-4 quite a bit in a 2000 Yamaha WR400F. It's marketed mainly for four stroke off-road motorcycle/ATV use.
Worked great with the wet clutch. The OEM spec's an SG oil for the cllutch/tranny, imagine Opti is something like an SG oil, no FM. It's marketed as a premium product, I never had any need to use anything else.
[ September 28, 2003, 10:42 PM: Message edited by: sub_zero ]