D2 Fuel Delivery Problem

Sounds like time for a new pump or rebuild. Have an extra you can try?

No extra pump. This one was rebuilt 2014 with help from Hal Houghton/The Classic Preservation Coalition.
-Snowman.

Any chance at putting a fuel pressure gauge in-line for testing? It really has to come down to only a couple of things. Is this a pump that has the atmospheric vent on the bottom? It's a stretch but mud wasps can clog that vent. As pointed out - restrictions in the tank, line, filter or pump itself. Heat/vapor issues. Venting. Weak or broken spring. Loads the pump while cranking but slowly can't keep up. Would be the same thing with a bad fuel pump lobe or arm.

Diagnose with a gauge and I bet we'll narrow it down.

I went back and re-read everything and I'm going to go even farther out on a limb here and say. You have no problem at all. Don't base that you have a problem on the amount of fuel showing in an in-line filter. They do not stay full. Run a gauge and I'll bet everything is fine.

Blind squirrel out on a limb? That is funny. Hang onto your nuts.

Thanks for the suggestions. The problem is that it will run itself dry, stall out and then not have enough fuel to restart. The pump is off now and we'll take it apart soon to see if there is anything obviously wrong.
-Snowman.

Any updates? Your fix might save someone else trying to hunt up their own nuts.

Nothing new. Pump is off the truck and we will try to bench test for pressure over the weekend. Other chores, repairs and family stuff going on. No rush now since we'll be out of commission for the July 4th parades.
Thanks,
-Snowman.

My other suggestion was a pinhole in the suction fuel supply, but you've bypassed all that!
Mechanical pump with bowl, glass or metal?
The top of the mechanical pump can warp where it seals that bowl. In fact, I suspect this is a design feature since it's all made of "amorphous" pot metal. Great stuff! Time for a new pump.
An electric fuel pump would've cut this problem off at the legs long ago.
Let us know what you find.

Yes, we have bypassed the truck fuel line. This pump has a glass sediment bowl. Like Blindsquirrel suggests, I think we'll re-install the pump and put a tee in the line to the carb with an old pressure gauge to see how much pressure there is at start and if it drops off after a while. Our gauge won't be very accurate but it should show if there is a drop in pressure - I think...
-Snowman.