The clutch operation is pretty simple and you should be able to see the problem if you look closely at how it all goes together.
The clutch is built sort-of backwards, so that the declutching stuff can be on the end of it. Many older bikes (and some current ones) run an actuating rod through the centre of the shaft the clutch is on (normally the transmission mainshaft) - this way the outer end of the clutch is being forced in by the springs and declutching forces it out. Servicing this type of clutch is a bit easier since you don't have to pull the whole thing out to access the plate stack.
That cutch rod has been troublesome on many bikes, so this "reversed" type was designed to put the declutching mechanism right on top of the stack, mounted in the cover. You can't see the cluch being released - the cover has to be bolted on to do that. That makes it a bit tough to diagnose a clutch that won't release.
The four springs push outward on that spider thing, which is bolted to long prongs attached to the rearmost plate on the clutch pack. This squeezes the plate stack together and makes the clitch "clutch".
So you don't need the cover on to see why a non-clutching one is malfunctioning. It should be locked up solid until the cover mounted cam etc. presses in on the throwout bearing.
It sounds like something is hanging up the pressure plate at the back, not letting it pull tight against the plates. The spring bolts are not an issue, and overtightening these will just strip then threads (bad idea) while too loose may allow them to work lose... if you fail to notice this a bolt head can damage the inside of the clutch cover.
If you remove the clutch you can try assembling it without the plates, the pressure plate should drop pretty deep into the basket and if it won't, look for the obstruction. Make sure no inner tooth plates are binding on the centre spline. Ensure the odd plate is in the right place, as I recall it goes at the innermost position. It's worth stacking the steel plates against each other and making certain that if there's any dishing (usually there is) all the plates are facing the same way. I've never seen new friction plates dished, but maybe check them too.
Check the splines and basket fingers for rougness. Both can develop "steps" or indents where a plate has sat for a long time working against the alloy as the engine turns and vibrates. That can cause slipping and nonlinear clutch action whan new plates with sharp unworn corners on their teeth grab on these indents along the spline or fingers.
The clutch should be locked up solid with the cover off, loosening the bolts until the springs are unloaded should declutch it enough to allow the spider to turn in the basket.
