Honda makes a recommended trans oil that is available at most Honda powersports dealers. http://www.extremegokarts.com/honda-hp-trans-oil-p-1121.html?cPath=4_3_30
I’ve run Motul trans fluid without much noticable difference.
Two things though:
1. The clutch cable should have a bit of slack in it since most kart handles can pull the cable too far and the plates of the clutch can be pushed out of the basket. Ask me how I know, kerblamo. I adjust it so when the handle is fully squeezed the plates have just barely disengaged.
2. Use the stock springs, I think the rules even say the clutch has to be stock. Make sute the revs are staying up, I try to slip the tires more than the clutch when possible. Stand on the gas and let the clutch out over half a second or less.