Leaking screw in Petrol Tap

If you purchase a new part and it does not do its job then it is unfit for purpose, return to manufacturer. In fact leaking petrol makes the tap unsafe!

Would PTFE tape around the thread be a no-no ?

The seller (whom your claim is against, not the manufacturer) can rather easily say the fault lies in the part you screwed it into.

Seal the threads with tape or sealant.

Wayne, 
The only sort of thread joint that seals is a male tapered thread in a straight female thread. Used by gas, water, hydraulics etc.

Never seen a petrol tap with a taper thread, for some reason they all seem to be a straight thread, which will always allow petrol down the thread. 

So the seal is made between the boss on the petrol tank and the top flange of the petrol tap. 

Fibre washer usually does it. 

The mistake some people make is to add a plain washer as a shim because the tap handle is pointing in an un-usable position. 

Then there is a leak path again, between the shim and the tap or tank. 

​​​​​​Are you trying to seal with a dowty washer? Try a good old fibre washer. 

Can you post a photo of this problem tap? 

Peter

Ive found that some of the taps dont have a boss they have a nut so you can adjust the tap position, however this lets petrol leak down the threads, even if you seal the "nut to tank" with a fibre washer. I tried a downy washer but in the end bought a tap with a boss!
Dan 

Unfortunately modern pipes often do have parallel threads sealed only by tape.  It's common (indeed normal) with central heating radiator spigot connections.  The make thread usually has saw marks along the tips.  This is to drag the PTFE into the joint.  In my view It's a terrible idea.  But no doubt much cheaper to mass produce than a tapered thread.  And if it leaks (which it sometimes will) you can't stop it by tightening it...
You might try hacksawing the thread tips to pull PTFE into the joint.  Or maybe use yellow PTFE tape.  It's available from plumber's merchants and is intended for gas fittings.  It's thicker than the white stuff.

Morning,

This will fix it:

https://threebond-europe.com/

Good luck.

Regards 

Steve