The 205 can be tricky to re-assemble with that big spring pushing the diaphragm away from the bonnet. I like the Sprinklerguys answer. If he's right just open it back up somehow. You'll know what to do. If it breaks off, time for a new valve. No you don't need a second washer? Also make sure there isn't any debre in that port. On occasion I've seen that valve re-assembled wrong so the diaphragm itself is blocking the port. You may have to bonnet turned slightly out of position. No matter what you need to take the bonnet back off to find the problem. Good luck!
If I can't fix it, it's broken!