Hi i have also just got this problem with it spitting out the carb on my 1900cvh engine, I have changed the black box on the dizzy and cleaned it up but have no result.
I was told at work that it could be an air leek so i changed the manifold gasket and started it up tonight and it does still not work.

The strange thing is that i was using it down brands hatch and was fine but as soon as i drove it the weekend the later the problem started and got worse.

If anyone could help i would be very greatful.