Over fueling 1.8t

Hi all my mk1 Gti 1.8t 20v has been been over fueling slightly for a while now but over the last few days I have been re under sealing the underside of the golf. While I was doing this I thought it would be a good idea to replace the 35 year old fuel tank this then lead to me fitting an uprateed fuel pump (Bosch 044) and all new beaded lines/fittings. So now the small over fueling problem has turned into a large over fuelling problem. Has anyone had the same problem? Or any idea what could could be creating  this problem.thanks in advance.

Over fueling?  As in Gas is leaking out somewhere?
Usually Filler neck rusted or vent hose loose, on the Gravity valve, or the Sending unit seal.

It's running rich. Dark smoke coming out out the exhaust and smells like un burnt fuel. It's also not idling very well. There are no leaks and the filler neck is new.

Carb, or injected?

With injection Vacuum leaks and then timing, and Duty Cycle adjustments go a long way to keeping it running right.

Now with the Injection there are 2 types CIS and Digifant
so CIS has stainless Steel covered injector lines from the airbox to the head.

Digifant has a fuel rail and the injectors are inserted in to it.  

Each type of injection system has quirks, so knowing which type you have assists us as well.