I don't know if the xs400 maxim and other ones are identical.. BUT!
On the maxim you pop off a plastic cover on the side cover and beneath it is a bolt with a nut on it. Inside that bolt is a screw.
To adjust it, you loosen the bolt(you might hear a pop, thats ok as far as I know, its the cable popping loose), and once the bolt is loose you you can adjust the screw. You screw it in until it seats(Just until it seats, you should not need to force or torque it at all). Once it seats you back off a half turn I believe? (180 degrees of the screw). Then you torque the nut back onto the bolt.
Then you take off the side cover, reattach the cable(if it popped lose when loosening the nut) to the spring system and put the side cover back on.
This should set the engine side of the clutch adjustment.
HOWEVER.
It could be that the cable has stretched. If you adjust everything to 'spec' and its still not engaging until very late in the release you may need a new cable.
It only takes a few millimeters to put the clutch out of whack.