with this very problem I have fixed it both times by replaceing the rusted line

pull it off and slap it on the cement one time to knock the rust loose

i counted over 37 pin holes and stoped counting

I have found a few ecentrics worn with a hole cut thru on the rub area and only moved the pump arm slighty

lots of older carbs tend to leak gas at the core plugs/jet wells in them,they need rebuilt and epoxy to seal them up good

the newer gas does not sit very long before bad and is even harder on the rubber seats/hoses in the system

if you have changed everything else,then I would lay my $ on the pin holes in the main line

after replaceing the line on mine,all the fuel delivery problems I had went away and would then keep the filter 1/2 full at all times and a couple days at a time

good luck