i recently fitted mine from scratch,so there should be some photos on the thread FYI.
first thing i would do is remove the pin on the cable where it connects to the drive leg steering arm.
then move by hand the lever to make sure that the lever/leg has full room to travel from hard over port to hard over starbord .
it could be the slot through the transom has debris in it or was never big enough to get full travel.
the cable i think has 15-17cm of travel and should have a stroke of aprox 7.5 cm either side from center.
check this with cable disconnected.
at the cable sheath termination there is a threaded barrel that attaches the cable to the mounting bracket fixed to the transom.
there are 2 bolts that can be adjusted on the barrel to change the central position of the steering rod in the cable sheath.
at the other end of the cable is just a simple morse steering rack ,to change the lever alignment.
at the base of the lever is a small hole with 1/8' grub screw in it,remove it and then the lever arm can be pulled off the splined steering shaft.
you can then centralise the cable to the drive leg so it has 7-8 cm each way of travel.
then with every thing centralised push the lever back onto the in the vertical position and re tighten the grubscrew.
other things that can effect travel are the bushings in the external lever arm and ball fitting in the top of the gear
box,check for play,there should be almost none.
if there is excessive play then it is probably a case of removing the exteriour bellows on the steering lever arm where it exits the mounting bracket on the transom.
to do this remove hose clamp and pull back the bellows and tap out the pin holding the lever as a pintle,undo the 3 allen keys on the ball fitting,then the whole steering arm can be removed and serviced.
and nylon bushings are available from sillette.
are also easy to get made up if a non standard length
pm me if you need more info cheers alex
edit from the photos it looks like the cable sheath needs adjusting so the cable is centralised more to port.
undo the 2 barrel bolts and move the cable more to port to get the correct center point of travel