Pop Quiz

[shokenore]

Any ideas?

[gwh200]

Err...looks like a land mine.

[si tate]

Is it the first ever X box from the 70's.

[Ultimagtr21]

A plug/insert of some kind?

[BUSHWHACKER]

Part of the fuel filler cap?

[TeaMonsta]

Difficult to see because of the round plastic thing in the middle of the picture, but I reckon that'll be one of your side steps/running boards.

[muddle]

A thingy?

[shokenore]

Yep it is the inside of the fuel cap.

As I was filling up with diesel again I had the normal whoosh when opening up the cap.

On my return home I decided to take a closer look at the cap.
Some on here have mentioned about fuel starvation and some hard starting issues due to the cap not venting, and causing a partial vacuum in the tank.
Some have also suggested drilling a small hole to allow the cap to breathe.

After some pondering I found the the outer grey and pale yellow parts will separate, leaving you with the pale yellow part as pictured.

If you look at the picture in the centre is a cross made of plastic ribs.
After a bit of a clean the material to the sides of the cross is actually a very fine mesh.
Also built into this part is a sprung valve.
Almost like the type of features you might expect on a cap that was designed to keep fuel from leaking out but allow air to leak in?

This has all been cleaned up in diesel and put back together.
So will the tank now breathe?
Time to do some miles to see if this has worked and save me drilling holes in the fuel cap.

[BUSHWHACKER]

Yep, it's to allow the tank to 'breathe out' as the breather valve on top of the tank can only 'breathe in'.