Fuel cap vent

[Ziggy]

My Triumph TR6  injection had a non vented fuel cap seal, which when opened released some pressure. I was told it shouldnt be non vented and put  a small hole in the cap rubber, so now there is no pressure. The car runs just as well, but I do get a whiff of petrol fumes now and again, is this normal and should it be pressurised or not?

[Pete Lewis]

well early or late   the  early shows a piped breather out thro' the floor 

all tanks need to breath somehow be it a open pipe or a cap with  hole or a cap with a biased valve fitted (if triumph ever did that ) 

as a later solution to rolled over spillage control 

https://rimmerbros.com/Item--i-GRID600041  shows a breather tube   the later version does not 

Pete

[Ziggy]

1 hour ago, Pete Lewis said:

well early or late   the  early shows a piped breather out thro' the floor 

all tanks need to breath somehow be it a open pipe or a cap with  hole or a cap with a biased valve fitted (if triumph ever did that ) 

as a later solution to rolled over spillage control 

https://rimmerbros.com/Item--i-GRID600041  shows a breather tube   the later version does not 

Pete

Its a 1973, so late model. So I guess the cap should have the breather hole in then.

[Mathew]

This has got me thinking, rare i know. Spitfires have a breather tube through the boot floor. Mine has fuel injection with an electric pump and a return line. I plumbed the return line into the hole that was the breather. Do i now need a vent hole, say in the filler?

[PeteH]

8 hours ago, Mathew said:

This has got me thinking, rare i know. Spitfires have a breather tube through the boot floor. Mine has fuel injection with an electric pump and a return line. I plumbed the return line into the hole that was the breather. Do i now need a vent hole, say in the filler?

I suspect the answer is yes. If the tank is unvented, it can lead to fuel starvation. Early Ford Escourt`s had a vent (location) that was prone to being blocked by road crap. You knew when the car started to hunt and on rare ocasions stop altogether. The answer was to run with the cap Loose and clean the vent ASAP. Some resorted to relocating the Vent outlet, basically just a plasicky rubber tube.

Pete

[Pete Lewis]

some spitty caps have the breath hole in the rubber seal others have the tube 

but breath it must and on a PI with a hot fuel returning the volume of air and fuel will change as it heats up 

hot air expands and increases/creates  the pressure in the tank 

IE fuel  retuning takes on heat from the engine attached pump /distribution units  etc.