Tuning works on some of them yes. If the gas nipple is damaged or off in the slightest degree, they won’t work no matter how hard you tune them. You can buy new gas check and some parts from numrich, as well as clip the main spring and maybe get lucky as well. You can try to uniform the gas port and you may get lucky. You can polish the chamber and maybe get lucky and have it work as well. There are some of these guns that run like champs and there are some to run from.
@Here2Learn , if you can see this gun in action and it works, I’d say enjoy it. If it won’t work, or they hesitate to let you see if work, stay away. They are neat guns, they are not accurate guns, they can be finicky guns, they aren’t of any particular collector value either. They made a half a dozen different models of the same design trying to tweak it and get it to be reliable. They quit making it because they never could.