AK -74 Tapco G2 trigger/hammer set.  Armory USA reciever.    Follows bolts, but will stay cock when cocked by hand.
Any fixes or other advice.  This is my customers rifle and I have Duracoated it for him.

The disconnector's hook is too low or the bottom of the disconnector's leg is needs to be filed more so that disconnector sits more towards the barrel.

If you open the top cover and play with the gun little bit you will see that in live fire this happens:
1. you pull the trigger
2. trigger releases the hammer early, so the disconnector isn't forward all the way - as it should be.
3. hammer hits, rifle fired, and cycles.
4. because the disconnector isn't forward enough, it doesn't catch the hammer, hammer follows the bolt and fires again.

To fix it make file the disconnector's hook so it sits higher, and file the disconnector's leg(from the bottom) so that the disconnector sits more forward to the barrel.
Goodluckk.