i had this problem. put in a new pump, no help, suspected the worn cam lobe. installed an electric w/ prsr reg set at 3.5 psi (weber 2 brl carb likes this setting) between tank an mechanical pump. i originally ran just the elec but it would get hot and shut down. my elec is an as needed and only pumps when the mechanical fails to keep up with fuel consumtion. the two together are working great.
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