Straight Castrol SAE 30wt.
Your engine is too small on that!! Take a cue from those guys who put a 350 and a 502 Chevy on a motorcycle!! Get a 88-CID Harley engine on that thing!
Not that I am a ricer fan, but a Kawasaki that will pull 9K rpm all night will sure as hell slice and dice and cut and evicerate and fillet and puree and vaporize anything that gets under it. That would be kinda cool. Especially if you turned upside down and put a big-a$$ aircraft propeller on it. VIOLA!!! A helicopter!