Fuel Issue

[FIATCAN]

Hello,
Having issue's with my 1980 131. I think i may have a venting issue with the fuel tank, while driving for half hour or so the car begins to hesitate and bog as if the carburetor is lacking fuel under 3/4 or full throttle. I have installed a clear inline fuel filter and gas is visible. I can also here the fuel pump running. I then went to the gas cap and as I loosened it I hear a noticeable amount of air release. The car then runs normal after this.
I guess what i'm asking is how does the fuel system/tank vent? and would this be my problem?

Thanks in advance
FIATCAN
Maurizio

[mirafiori76]

Hi Maurizio,

Looks like the ventilation is blocked and the tank sucks vacuum. It's very possible that the ventilation hose is blocked somehow. It's the one on the side of the fuel pipe and it runs up to the roof and then al the way down. There is also a valve halfway in that same hose. Check both and your problem is possibly solved.

[FIATCAN]

Hello mirafiori76,
I have attached a few pictures. Can you show me which pipe/line i should be looking at?
What are the two white plastic pieces at the end of the lines, they are located on both sides?
thanks

[mirafiori76]

Hi Maurizio,

These are not the lines i mean. I meant the hose that is attached to the filler pipe. It's mostly transperent blue and after the valve it could be red. It runs up inside the C-pillar on the right side and then al the way down to the floor of the car. This hose is for decompreesing the tank.

[grahamS53]

Hi Maurizio. You could try running with one of those nasty temporary push in fuel caps, these never seal properly so will allow the tank to breath, but will still be better than running with no cap. Would prove the point prior to trying to find a blockage in a 30+ year old pipe
  I must say, from experience a tank normally only vacume locks from nearly full and once down below that there is enough air in the tank to survive,after the initial release, plus you say there is fuel in the filter so you would expect the resevoir in the carb to be full? But who knows eh? letr us know how you get on. G
PS if the vent pipe is blocked it only needs a small hole in the cap to stop it. G

[mirafioriman]

As an aside I notice this 131 has inertia reel rear seat belts

[grahamS53]

So does one of ours.

[Tas131]

As an aside I notice this 131 has inertia reel rear seat belts

Both of mine do.

[Henk]

maybe this helps?
regards
Henk

[FIATCAN]

The only pipe I found that was kinked was the the clear pipe that comes of the filler neck back into the top of the tank... I can't see how this will disperse air? I notice that once the hesitating starts if I stop and realease the cap the car runs fine. Is the cap suppose to be self ventilating? It is the original. Also in Henks picture (thanks) only what would Item #1 "seperator" purpose be, there are two?
I also did not see any pipes run up the "C" pillar.

Thanks

[Henk]

Hi again
I think the so called "seperators" are two mechanical vent valves, opening on pressure diff.
please see picture for a general working principle of tank ventilation

best regards
Henk

[Henk]

Having a closer look, the two separators might be the fuel traps (preventing liquid to go to the valve?)
The vent. valve should be nr. 4 /5, opening at too high or too low tank pressure