If I remember correctly the GT550 has the Kawasaki standard in-line 4 cam chain tensioner of the era.
It relies on a spring to put pressure on a blade, against which the chain runs.
Unfortunately Kawasaki thought it would be a good idea to put the spring at 90º to the direction in which its force must act (towards the fron of the engine), and to do this the spring pushes a rod which has a 45º chamfered end, which in turn pushes on a second rod also with a 45º chamfer.
What happens is that the friction between the 2 chamfered surfaces is too great or they get a bit stuck and the tensioner stops pressing on the blade.
There are 3 fixes available:
1: Hit the tensioner with a big stick and it will probably "unstick itself" and start working.
2: Dismantle the tensioner (very easy as it does not need to be removed), lubricate the mating surface of the rod which runs in the spring and re-assemble.
3: Get a different tensioner without the silly 90º system.
Fixes 1 and 2 are temporary as it will jam again !
NOTE: It could also be that the cam chain is too worn for a working tensioner to have the desired effect, in which case change the chain immediately.