Petrol Cap advice

[trickyrobo]

Hi All, first post so be gentle, lol! Had my early Bay since last November and its nearly all done now. I chatted to a couple of you chaps at the Oswestry Show the other week (Scotty?). I've just brought a mild steel locking petrol cap off the Just Kampers site that has not arrived as yet. A friend who has a splitty said he got a Stainlees one from elsewhere and he put a small drilled hole in the cap to allow for fumes to escape or to help the tank not contract due to vacuum???? I was a bit confused to be fair. I thought the whole point of a new cap was to stop the escape of petrol fumes etc. Can anyone expand on this for me, pun intended.
Cheers,
Pete

 

[Clem]

Petrol tanks are vented to allow them to breathe (the air/fuel expands with rises in temperature, and also has to allow air in when the fuel goes outwards to the carb), but most fuel caps are vented by design to assist this. Id fit the cap and crack on.

 

[trickyrobo]

Thanks Clem, I would of thought a brand new cap would have the right spec etc but thanks for explaining the thinking behind what my mate had said, appreciated.