Any motorcycle shop will have the nitrogen filling equipment needed to charge the shock. But, if I understand correctly, you are working with a shock designed to use air from a tire filling station, so I would just save a few bucks and continue to use air.

As far as swapping an old shock into a different bike, I would refer to the specifications for both the original and the replacement shocks and the spring rates. If they are in line with what you are looking for, and it fits, go for it. What you do not want to have happen is to get a shock with incorrect rebound and compression rates, a spring rate that is inadequate for the bike, as that will lead to porpoising/bucking in the corners, and could get quite dangerous.

 

my mistake: this shock i refurbish it's from a gpz 900, the same of mine!, (same bike)

my question is: it's possible after oil change , fill it with air and use it?

 

up?