Just as a data point, I had rich condition stuff, mostly on hot restart. I replaced the accelerator pump in my YF based on feedback I got here. It cured the condition. There was no visible tear in the old diaphragm, nor did it “feel” notably tough. I also checked the pump “bonnet” as per Jon G’s procedure while doing this jump. It was not warped.
All I can figure is that the old pump had a pinhole that I couldn’t see.
JW, your accelerator pump, while not being cracked or visibly pin-holed, may have swelled up / stretched from exposure to ethanol.
When ethanol was introduced to the fuel supply in Atlanta in 2007, it killed the original fuel pump in my Cadillac within 2 months. It stretched the diaphragm enough to where it would only pump half the required amount of fuel. No pin holes or tearing at all.
Since then, no problems in any of the carbs or fuel pumps made with the ethanol resistant rubber.
