I just picked up a 91 RS and when I put the bike on the center stand the rear wheel is not off the ground the center stand does not seem to be modified or broken and there no play in it and the rear tire is stock size 160/60-18 any ideas what's going on? what length should the rear shock be? thanks

Mine is the same as yours.

to be honest I kind of like it because it is so easy to put on the stand

I think that the mounting holes on mine are a bit worn, When I get around to it I intend to ream and sleeve them.

The K1100 centre stands did leave a bit less clearance to ground but I would not expect the rear tyre to touch. Maybe as suggested the piviot are worn or the shock length wrong which should be 15 inches. The K1100LTs have 4 small spacers between the gearbox and stand so maybe even some washers inserted there would be enough to help.

had a similar issue ....welded some more metal to the pedestal legs to stop mount interface so the fall of the stand doesnt go as far forward ....made it easier to get it off the centre stand as well .(thanks to alby )
i thought that the angle of the centre stand was going over verticle more than neccesary making it really hard to get it over the balance point ...especially with a high camber road surface that you would have to push against .
in the process it has raised the bike off the ground just a little bit more maybe 5 mm at the rear wheel
or as others have suggested possibly some washers between the bracket base and the gearbox mount points

Food for thought there Charlie I might investigate that on mine as it is a bit difficult at times but maybe its just a worn out old rider which is what I was thinking.

I'll have to check that out it does seem like it takes more effort to push it off the stand than my other bikes thanks for the idea's