As I see it, one of six possibilities exist (in no particular order):
- Viton needle tip not cleaned with non-residual carb cleaner so as to be compatible with gasohol.
- Fuel quality so poor that needle won’t seal. It sounds as though fuel is rusty, which suggests water is present, which suggests that the gasoline and ethanol have separated — you get the picture.
- Debris stuck in needle seat holding needle open. Did he assemble the fuel system with teflon thread tape? I bet he did.
- Float is leaking.
- Fuel pump is generating more pressure than owner has measured. In my opinion, 5 – 6 PSI itself is too much for that carb, and is certainly more than a 4-cyl. engine requires.
- Needle seat threads were not dressed with teflon thread paste, and fuel is leaking past them.