74 1.8 - fuel pressure regulator?, opinions. Options

[wonkipop]

car = 74 1.8 L jet (all intact).

problem =
out driving this morning - gradual then worse loss of power. no accelerator response.
pulled over. cut out. no idle. let it sit for a few minutes. restarted it. got it going.
got up road all right, but symptoms kept coming back, then going away. limped it home.
fun ruined for driving, but fun diagnosing started.

felt like your classic fuel starvation.

background. car has been recommissioned and back on road for about 5 months.
running beautifully.
fuel system entirely rebuilt. clean tank. new fuel lines. new fuel pump. new injectors.
all vacuum lines renewed. all ignition compenents renewed. except coil (which could be original, looks like it, but coil was tested and was a goody).

one thing = fuel smell in engine bay on lhs around air cleaner. comes after a few days sitting. had put this down to saturated charcoal cannister, feeding back fumes into aircleaner. have inspected all fuel lines etc thoroughly and no signs of any external fuel leaks/wetness. just a vapour smell thats not there all the time, just after sitting.

pulled everything apart today down there after getting home today.
checked everything. all tight, no air leaks. no bad hoses.

looked at pressure regulator. which sits right there under aircleaner.
i have no reason to think its not original and about 45+ years old.
and did not get replaced. looks great externally, but.........internally?

will get car into shop this week. where i can get some guages on it etc.
at home with car. nothing but basic tools.

but whats thoughts out there.
anyone had this one before.

[wonkipop]

think i cracked it this afternoon.

did some work at afternoon tea break.
pulled down the intake to the throttle body junction with plenum.

nothing obvious there, i had detected no air leaks with hose or cig smoke previously.
but come to think of it i had not been doing either of those things while it was in fault mode, i'd been listening for leaks after it had got to a stable idle situation the times i had gone over it.

i did three things only.

i cleaned interior of throttle body, slight little pool of oil from pcv valve hose.

and i pulled out the throttle plug which was lightly coated in oil and cleaned it.

and i thought how did that oil get there.

i found one of the screws holding the throttle body to the plenum was loose, but when i say loose, i mean barely loose. it turned maybe half a turn with screwdriver to tight, the other one was tight. so backed it all off, cleaned cone gasket. put it all back on square and tensioned it up evenly. i noticed that the gasket/joiner was maybe starting to go hard, (its been 46 years!).

i cleaned the tube from the aircleaner to the throttle body throughly. i gave it a look over with a magnifying glass. its still flexible. like factory fresh. no cracks.

so i put it all back together.

put it through the regime i had done earlier and the fault is gone.
no hunting (ok some, but very minor and i put that down to the adjustments done on monday to stabilise the idle, and the settings now need to go back). it comes up to even idle after fully warmed, no hunting or carrying on.

since then been out, started it every 20 minutes or so. let it come up to temp.
turn it off. done it 6 times - fault is gone. this would have induced the fault given what i had done over the last two days to work out how to make it happen.

so its down to one of three things or all three.
1.throttle switch connection dirty with oil.
2.cone gasket between throttle body and plenum leaking air at certain point of expansion and contraction in heat soak cool down phase after switch off.
3.there was an air leak between air duct hose from air cleaner and throttle body.

i'm going for #2 and searching out a new cone gasket/joiner for the throttle body air plenum junction.

i think what has happened is that particular part maybe has hardened up.
and engine vibration etc since recommissioning has caused one of those tensioning screws to back off and loosen enough to upset it. not much, but enough it seems.

if #2 is what it was it proves how sensitive L jet is to leaks (super sensitive) and that those leaks won't necessarily be there when its cold or when its fully hot. but they might develop at a moment when the two materials expand or contract differently during a cool down phase.

i'll be driving it out on the road to the workshop tomorrow to reset the mixture, so i will see if this holds up on the road tomorrow.