At the next meeting, even with the new pump, it was hard to fire a few times. Same symptoms, fired up quickly but then quit after a few seconds. Then last week we tried to test run it, would not start at all.
I have finally been able to determine the area of the problem, it's to do with the ignition system & probably related to battery voltage.
I tried firing it in my garage on just the bottle, same issue. Then I replaced the MSD 10-plus with an MSD 7 powered from a seperate battery. It fired right up & ran as long as I fed it. Result!
Of course, the driver starts jumping to conclusions, it's the 10-plus, we need a new one, we need a mag.
So I wired the 10 back in with seperate battery. Started & ran on the bottle easily.
So it's definitely either an issue with the wiring eg ignition switch intermittent or it's the battery voltage dipping disabling the ignition.
I can deal with it now I know what's going on, I have a background in electronics.