Assuming you've done that, then the clutch springs must be torqued up appropriately and within spec.

The clutch MUST spend 24 hours soaked in oil prior to their installation, this means to take each clutch plate out on their own and bathe them in a layer of oil for 24 hours.

The clutch is actuator by the cam arm, two push rods separated by the ball bearing.

However, this is used to disengage the clutch, which wouldn't cause it slip.

If it's been set so that it's never engaged, then this would be where you look.

First starting at the clutch basket, you want to ensure the screw and nut have been adjusted appropriately.

Once you're confident that's been done, then you adjust at the cam arm.

And once that's done, you make your final amendments to the clutch perch.