The Bad, Good, Bad news - Engine problems

The engine in the 62 has never run as smoothly as I would have liked. I have spent hours resetting timing, tappets etc and still it feels lumpy and juddery once warmed up. My friend who built the engine with me came around yesterday and we logically went through tappets, timing, points etc but it made little difference. We concluded the problem lay on the fuel side and so today, one at a time, I replaced the fuel cut off valve, fuel pump and then all that was left was the NOS carb that I fitted.
I dug out the original carb for the engine, took off all the crud from the outside and then stripped it and cleaned every part of it. As soon as I put it on the car and started it then the car sounded as I would expect it to with no uneven running. It was smoking heavily so I rest the idle and volume settings and the rich running and smoking disappeared.
I took the car out for a quick spin, what a transformation - it ran like a train all the way to the next village, I turned around to come back and then 150 yards away from home the engine just died. I managed to get it around the corner into our road and could not get it to restart.
After fiddling with it for over an hour and changing the wire from the coil to the points as it had a crack it it (desparation as there was spark at the points!) I managed to get it going again and into the garage. It started OK later on but I have no confidence in it and have a journey to make on Friday morning around one of the UK's busiest stretches of motorway to the VolksWorld show where it is due to be on display.
Potential culprit at the moment if it remains as a fuel problem will definately be the carb as I swapped back the fuel pump\cut off jet and so could be:
- May be the accelerator pump - I'll strip the top off the NOS carb and look at how much fuel it pumps up through the drilling compared to the one on the car and change the diaphram if needs be.
- The float needle valve - I put in what looked to be a good free moving one when I rebuilt the carb as the original was sticking but it was also stuck shut when I took it apart again - only problem is the carb was full of fuel so it is unlikely to be the problem. It's an easy change so I will do it anyway.
- probably crap adjustment of the idle\volume screw settings by me, although I followed the VW manual for the settings.
Anyway, keep your fingers crossed as I don't want to let the guys at VolksWorld down and have already found a trailer in case I have to resort to that to get it to the show.