Fuel pump options, Staying in its original location Options

[emerygt350]

I am having a very specific issue here. Pump no longer holds pressure after shutdown. Original location, original three port pump. It still pumps great when running, but no longer holds pressure. Need to fix that and quick. Do I have to replace it or can it be repaired?

[wonkipop]

interesting read @emerygt350 .

i think you are right.
its the section of line that pops out of the firewall and feeds to the pump that is the cause of vapor lock issues in 914s with original fuel pump location. thats the bit of line where the fuel boils. it is subject to heat radiation from the mag fan casting. due to conductance all the heat in the engine flows to that fan shroud and radiates from there after shutdown. while the engine is running however the mag casting is cool due to all the air flowing through it. its after shutdown it becomes a heat sink.
that fuel line sits about 6 inches away from that heat sink.

most fuel pumps don't work so well in suction. they are more powerful on the other side.
so the feed line is a kind of combination of gravity flow from the tank and the weak suction of the pump. thats why its a bigger line than the return.

your speculation that its gasping at vapors is fairly sound i would say.

your tests indicate its not back flowing through the check valve in the three port pump.
thats a little spring loaded pin with a rubber tip on the end of it. most are perished and don't hold pressure anymore if they are still on the car. as others describe above.
if they are losing pressure straight away after shut down thats because their check valve is kaput. thats not the case with yours. test proves it.

i have pulled apart two three port pumps completely.
the top three port section is where the check valve is and you can get that off without going deeper. and you can carefully take it apart if you are curious. the critical piece is the pressed tin crimped cover on the end which holds the spring in. its easy to damage getting it off and then trying to get it back on.
if you want to try its all here.

http://www.914world.com/bbs2/index.php?sho...350416&st=0

but i don't think its your problem.
your injector ring is holding pressure.
i think your logic as to what is going on sounds right.

i have the fuel pump in original location.
have resisted the unoriginal modification. (IMG:style_emoticons/default/biggrin.gif)
but i now have metal fuel lines in the tunnel and almost to the pump.
and i have wrapped them with a very effective reflective insulation wrap.
have had no problems with vapor lock since doing that.
interestingly i never experience vapor lock before doing the conversion to metal lines.
only after. so the metal lines were worse than the plastic originals in terms of heat absorption. insulating the metal lines got rid of the problem.