Chris Hogg Wrote in message:
On 26 Jul 2018 11:40:03 GMT, Tim+ wrote:

About 5years ago the fuel cap on my McCulloch Trim mac 250 started leaking
fuel through the vent hole in the cap for no apparent reason. I bought a
new cap and all was fine until today when I realised that fuel was dripping
out of the vent again.

There are no apparent cracks in the cap. The central vent “plug” looks to
be composed of partially fused metal beads. Any ideas why the vent is
failing like this? It just seems to “happen” for no apparent reason.

Is there any way of restoring its fuel retaining properties whilst
retaining its air admittance properties? It’s no big deal as replacement
caps are available on eBay but I’m just curious as to how it works and why
it fails.

Tim

It's not just sunshine and hot weather causing the pressure in the
fuel tank to increase and forcing the fuel out, is it?


Did cross my mind but even in the shade, just tipping the strimmer
causes fuel to start dripping almost immediately, even after cap
removal to release any residual pressure.

Tim



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