I think I have the culprit in mind but will ask anyway since there are more experts here than I am.

My fuel filter tower pressure gauge never indicates any pressure when cranking the main engine with the pony motor.
The filter tower has three new elements and mounting rods. The fuel transfer pump has a new shaft and new shaft seals.
The bypass valve spring is new since the previous one was corroded in two. The Bakelite plastic bypass poppet looked fine.
Unfortunately clearances on the transfer pump gears was not checked when the pump was dissembled.

Even in this condition there has never been a time when the main engine would not start.
I have started it on some 45 degree days. I never use ether. It just has to be warmed enough by the pony.
When the main engine starts the fuel pressure gauge dances around. You might even say it vibrates.
After a while it settles down to where it indicates to the low side of the caution band on the gauge at normal governed speed.

So, my suspect is the poppet valve in the transfer pump bypass or the new spring is not exerting enough pressure on it.
Am I on the right track here or am I missing something?

Thanks.

Patrick

Check housing seating of the pressure relief valve.
Verify the pressure gauge is working properly.
If neither of those are at fault I would suspect internal pump clearance issues.

It’s been a few years since I bought one for a pre 1960 engine but seems like some of the poppets had a rubber seal on them instead of being a hard plastic like the later ones are. I remember that once the rubber got stiff, they didn’t seal well.

If no rubber sealing surface on the poppet, any erosion in the seat surface will result in worse leakage. You may need a new poppet and or carefully resurfacing the seat area.

The fuel tank is full as of a couple of weeks ago but even when it was not it acted much the same way.

Hi Team,
the hard plastic relief valve poppets were problematic back in the day and were a known trouble source.
A piece of crud--dirt, lint, hair etc. held them open and if left long enough erosion occurred at the crud site and gave low pressure issues.
Rust pits on the pump body valve seat area required facing on emery paper, filing in the field and emerying or machining in the Dealer shop if too deep for a quick touch up.

I used to wad punch a suitable sized hole in a piece of fine emery or wet/dry emery paper to put the poppet guide end thru and resurfaced the poppet valve face ring area ---from new the poppet sealing ring area is actually rounded so it has a line contact. Afterwards you need to reduce the area of the face carefully with a fine warding file, or else the surface area is larger and so the surface pressure is less and lower fuel pressure results- stretch the spring a tad and see what you have.
Sometimes a quick touch on the emery will show an unseen worn, indented spot on the poppet seat area.

Cheers,
Eddie B

Thanks all. It looks like I'll be pulling the pump off again.

My gauge on my 12 never shows good pressure when cranking with the pony. Pump was near new. 0 wear. I had already stretched the spring. Ordered the poppet without asking the price. Couldn't be much. $48.00 and didn't change a bit. Live with it. I do have a 1/2 inch, in line screen filter that helps with crud. Hose clamp style.

One important thing to do is when redoing a fuel system is to clean ALL lines and ports with compressed air, I have even had to use a long piece of wire to poke through some plugged tubes in the filter housing to open them up.