i agree witht he above poster. I have raced other brands for a while now and the mugen clutch has a very soft spring setting.

the trick is to not over tighten the spring. even half a turn on the mugen spring can result in too much tension. Initially do what the manual says. tighten the spring flush to the pilot shaft nut. as the spring gets looser you can go half a turn or 3/4 of a turn in.

also this clutch responds with significant slip if you shim too much of a gap between the shoe and the bell. i found .4 to be the maximum, .5 for me resulted in slip.

finally what i did with the flyweights is i sanded down the inside edge that hits the pilot shaft when the shoes move out. check yourself, move the flywheights out and notice the edge that hits the shaft, then cut this edge down so the fly weight can move all the way out, doing this helps to get a little more movement from the shoe towards the bell.