28-02-14, 01:57 PM
If adding a bit of choke helps, that really points towards mixture as the problem.
Have you checked the fuel levels in the carbs? It's a slightly fiddly job but might reveal where the fault lies. (You are correct, the few seconds clattering from the fuel pump is normal after the bike's stood for a while as it tops up the levels lost to evaporation.)
What do the plugs look like after a run?
If neither of those ideas bear fruit, it might be time to stick a compression tester on it.