vented or non vented fuel cap?

[Megamatt]

Hi all,

Can someone help me determine the right fuel cap to use on my FB? I have two options - a non-vented, non-locking cap which came with the car when I bought it and another locking fuel cap for which I do not have a key or an idea on where it came from (thinking FE or FC). My preference would be to have the security of locking it, plus being stainless will save me having to paint the other one. My concern is should it be vented? Guessing if it is not, as the tank fuel level drops it will eventually create a vacuum and affect fuel to the engine?

If it should be vented, and both mine are not, what are my options?

Thanks,
Matt.

[Blacky]

You need a vented one mate, Rare Spares sell them .....