Whilst you are fiddling around install an electric fuel pump, easiest and cheapest fix to a similar problem I was having. Accept you have a stainless tank, (sadly mine is not), but the old mechanical pump didn't seem to be able to cope with even the least bit of contamination. Added bonus is the comforting whirr when you turn on the ignition.

1978 Morgan 4/4 4 Seater Molly
2015 Merc C250D Helga