Series 6 Gazellle Running VERY Rich.

[kevin]

I have a series 6 Gazelle auto that has always run rich since purchasing it, but it has all of sudden has got a lot worse and almost undrivable. It has the Zenith 34IV carburettor and I have fitted a new gasket and seal set including the o-ring around the venturi as well as a new needle and seat. I have fitted a NOS AC fuel pump kit and the pump is working at 2 lb's pressure. Still that made no difference and a fuel pressure regulator fitted and adjusted to 2 lb's. No change. I have found another 34IV carb and swap over the top and bottom halves but still no improvement. It is very hard to start but once started and running it chugs and runs very rough on idle and blows black smoke. If I hold it on high revs it seems to run OK. If I bend the rubber fuel line and cut of the flow it settles down and idles smoothly till it empties the bowl. I have had a mechanic that worked at a Rootes dealership in the 1970's look at it but after spending many many hours on it it has him beat. Any advice would be greatly appreciated. Also the factory 1725cc Rootes Service Manual does not state the jet sizes, if anyone can advise me of the correct jet sizes for a 1966 Series VI Gazelle Auto I could check the jets and if needed solder up and redrill.
Hoping someone can help, Cheers Kevin.