Petrol tank breather pipe

[andrewdmoore]

I am still trying to find the cause of a misfire on my 71 sprint, which only starts if you accelarate hard after 30 mins driving. My thoughts turned to a possible blocked petrol tank breather pipe, but try as I might I couldn't find one.

There is a small diameter metal pipe in the neck of the filler that leads back into the tank, but surely that can't be it as it would be sealed from the atmosphere by the filler cap.

My workshop manual has details of an anti-evap system on post 71 cars but mine doesn't have this either.

Any clues or advice please?

[types26/36]

Andrew,
If your car is a domestic spec (U.K.) the tank is vented via the filler cap, if you open the cap on the underside you will see a small hole in the plate, this is the vent.
If you have a federal I do not know how it is vented,may be some of the guys in the states know.
Brian

[mark030358]

If the vent was blocked you could/would create a vacuum in your tank and it would crush in extreme cases. Can you hear a "woosh" if you take the cap off?

cheers
Mark

[Mohe]

you can test if your breather is blocked. drive the car with the filler cap open to let air in - if the problem dissapears the breather looks like the culprit.

Mohe

[andrewdmoore]

Thanks for the advice. I found took the filler cap took it to bits & blew down the hole & no blockage. But surely a 0.5mm hole doesn't let enough air in when you've got your foot down or have I got a non standard cap mechanism?

[types26/36]

surely a 0.5mm hole doesn't let enough air in when you've got your foot down or have I got a non standard cap mechanism?

Thats plenty big enough and it sounds like a standard cap to me.
Brian.