My darn scale battery went out I was going to weight the stock weights to see for myself but previous threads state that 12g for stock rollers. I think most tuners go for a total weight of 27-30 grams total. I'm too cheap to buy a bunch of roller packs to tune in the weights but 3 stock (36g) seems to work well for me, less may be better though! I live in a hilly area so I needs low end!
Although the 27-30 g's work for them doesnt mean it'll work for you because they have pipes, bigger cylinders, wider belts, etc. to make the lowend suck I'm thinking if you shoot for 30g's with a stock belt and stock setup you'll be able to do wheelies!!!!!! hahaha