Update: fuel delivery problem, 250 GTE

[afwrench]

Don't know if this applies but I think I remember a vexing fuel delivery problem on this forum being traced to a fine crack in the pick up tube in the tank. It sucked air and caused a starvation problem. Just a thought.Good luck,Mike

[Zanny1]

Zanny,

Both the mechanical and electric pumps have one-way valves that keep fuel from draining back( to the tank). They also keep fuel from just circulating in a circle between the mechanical and electic pumps and not filling the carbs. Usually when our cars have a fuel delivery problem, one of the valves has/ is malfunctioned.

You can by pass always the mech Fispa mech. pump without a problem. Check regulator if right pressure shows up (Steve`s pic above)
Do you have the same regulator like Steve´s ?

Cornelis

I think you may have nailed the problem, Cornelis.
I spliced a fuel pressure gauge between the fuel bowl/regulator and the front of the fuel rail.
The needle on the gauge 'bounces' between 0 and 3 psi. No amount of engine speed could get the needle above 3 psi or make the needle steady. Adjusting the fuel pressure screw in or out makes no difference.Turn on the FACET fuel pump, installed in place of the original FISPA electric unit, and fuel pressure is steady at 4-1/2 psi. So it appears the mechanical pump check valve(s) don't work. The rebuild kit had new valves, but they did not look like the originals. Stupid me, I put the old ones back in. Even if I go through all the trouble of taking the pump apart again, I have no idea how to test the thing to ensure it works like it was designed.
Yes, my regulator looks just like the one in the picture.

[250GT]

I Published this once before, found as blog on RPM Vermont side Autocraft:

".I have purchased kits from different suppliers and the internal components are slightly different but I have figured out how to make them work reliably and with all kinds of different components. It would be easy to blame the ethanol fuel but so far I have not seen that to be the problem.
The camshaft that operates the fuel pump on V-12 Ferrari’s has very little lift, so the first thing I do is replace the rocker shaft pin and make sure there is no play on the mechanism. The solution to this problem is very simple but is a trade secret. Next I clean all the parts and send off the top cover and the hardware to be re-plated. I have tested the original check valves against ones sourced from a tractor parts supplier as well as the aluminum ones that come in many of the current rebuild kits for the FISPA pump and have found all to work well. To my knowledge, the original check valves no longer exist so I am happy to find that other styles work just fine. The issue I have found is that the replacement diaphragms are the source of the headache.  The diaphragm material is a black single thick layer rather than the 3 thin layers on the red original equipment stuff and in some instances it does not seem sealed properly at the head of the operating rod. Also, they seem to make too much pressure. I realize that the regulator should reduce an over-pressure situation but the red material consistently makes less than 5 psi where I have experienced  the black material making as much as 12psi! With testing the black material for leaks at pressure, I alter the return spring to get the pressure where it belongs ".

C.

[Zanny1]

Got (2) Facet electric fuel pumps installed this weekend. Not a job for the faint of heart - there's plenty of space to put one pump in but very little space to put in two. Biggest challenge is clearing the fuel filter with the 2nd pomp and connecting all the fuel lines adjacent to both pumps. Fabricated a heat shield that covers the bottom of the pump assembly and lines. Flushed out the lines before connecting to the fuel rail......plenty of debris came out as a result of replacing hoses, fabricating new lines etc.
Once installed, I bypassed the mechanical fuel pump altogether and simply connected both hose ends on each side of the mechanical pump.
It works great, is quiet, and delivers 4 psi at the fuel rail. Drove the car 50 miles, put it back on the lift to check for leaks..... all looks good.
Now on to get the rear suspension in order. Thanks to all for your valuable comments.