I just purchased a used, non working Thumper that sort of spurts air when I cock it (as soon as the mechanism returns "home"). There's a hole in the piece where you adjust the reg that I'm not seeing in any of the pictures. I think this is the problem. It's a V2 as far as I know. I've lubed the hell out of it with vaseline and put Gold Cup in the ASA. If I gas it up and let it sit for a few minutes it will fire once, but that's all.
Also, the bucket changer likes to come loose after a few "shots" is there any fix for this? I'm using LeLands.