was very similar.
would run....low rpm
ok.....hooked it up and engine
would eventually quit.....almost like clockwork......checked hoses, return, filters primary and secondary.....what I found, by holding a strong light behind the bowl of the Racor
were tiny "champagne like bubbles". I removed the racor assembly and there was a small crack in the plastic.
Replaced the bowl...problem went away.....
Another problem I have seen is when the racor element gets clogged
the mechanical fuel pump
puts such a vacuum on the filter that it sucks air......If your reurn line does not go back tot he tank...the air will accumulate in the secondary filter