had a quick go at it earlier. couldnt get much done though as i have tweaked my back and had shooting pain down my left leg all day, coupled with the rain its not been productive. so i picked an easy bit and fiddled with the bowl on the pump. when i went to take the bowl off it was suctioned on and took a wriggle to free. checked the seal and it seems to be seating properly and the bowl seems to be fitting properly. yet whenever i put it back on and tried to prime the system it wouldnt even begin to fill before it suctioned on again and stopped the fuel flow. i took the pipe off the carb and tried to see if i could pump some fuel through and nothing was getting that far.
so i think that points to the problem being further back. i shifted the tap a bit and its harder to turn one way than the other, which is odd. so perhaps the rubber (i think it was rubber anyway, i know some are cork and it was a long time ago that i opened it up) seal has shifted and it mostly blocking the ports. i will bypass the tap tomorrow and see how it behaves. i would like to keep a tap though, i will have to see if there are other alternatives in case the military one is damaged.
the plumbing is all the right way round, it was flowing well enough until yesterday.