When I first bought my van, that had similar issues. It used to be difficult to start when hot, would sometimes cut out after a run, etc, etc. It had had a new pump fitted so I discounted that. I then checked everything else, filters, new fuel lines, and all seemed well.
Then I read about fuel starvation in the wiki and from other peoples posts on the matter, so I then removed the fuel pump and measured the operating rod and it was worn down, should be 100mm long I think [you need to check for yourself] if its too short, the pump cannot feed the carb properly. A new one fixed the problem.
Hope that helps!