Lol, the bolts not upside down is it? Because I have seen that a few times. If you left it cocked while in storage you may have squished the main spring and you might need a replacement.
To start troubleshooting, turn the velocity adjuster in the back about half way in. Then adjust the reg all the way down till its under say 200psi or it chokes. Slowly turn it up and fire a few shots untill the speed comes up. If it doesn't really come up make sure the bolts facing the right way if its a one hole bolt or replace the main spring because its probably shot. If you are up for it you can take the lower tube internals out and make sure they are smooth and not covered in gunk and slowing the firing cycle down. If theres enough friction down there from old paint or bad oil/oring/etc then that could cause the problems you are having, this is an issue normally encountered with blowbacks but it could be whats going on here.
Everyone says "Well maybe i'll make a difference",
Thinking they've got plenty of time
But you're squeezed a little tighter everyday
Finished before you can commit a crime