have you adjusted the clutch push rod, if the rod adjustment is lifting the clutch off, it doesnt matter how much slack there is in the cable.
my normal setup is to unscrew the adjuster, or slacken so i know it isnt connecting, then slowly screw it in so it is just touching, then unscrew about 1/4 of a turn, then lock it up, then adjust the screw adjusters, 1st on the handle bar, leaving some room each way for adjustment (i know on my old brits, if the clutch plates swell up then you need to take up all the play so the clutch will release, so its a rule of thumb for me)
next adjust the casing screw adjuster so you end up leaving about a 1mm of play at the lever end.