Don't, whatever you do, quote me on this, but I think I touched on something like this with the 1998 Fiesta I used to have when I was having trouble with the EGR valve. And, I have no idea if it is relevant to the Puma and I will probably be corrected by someone more knowledge... but here goes..
There was like a 'box' which contained something like a carbon/absorbing material. This was something which would absorb the fumes/vapour from the pertol tank (I think via a breather pipe in the tank).
Under the bonnet, there was a small black 'box' with two small rubber pipes connected to it.
'IF' I remember correctly, some kind of vacuum would 'purge' the fumes from the 'box' which contained the carbon material and dump the fumes into the engine air flow/inlet or thereabouts.
I have no idea if the Puma has this type of system, but if it has, then you problem may lay somewhere around that area.
My second Puma stinks of pertol sometimes, but that comes from the filler cap as the rubber seal is not too good.
