The leaks I've been blethering on about only refer to when the engine is running, so if your leak occurs only when the priming bulb is squeezed, then its got to be a leak between the bulb, fuel filter and then on to the injection pump i.e on the low pressure side of the system.
Therefore, we need to inspect for perished or rubbed pipes, (the latter being the most likely), a filter incorrectly replaced or leaking pipe connectors (rather unlikely that one, so long as they have been carefully removed and replaced).
We're closing in Ok, the leak is when the priming bulb is squeezed, also when the engine is running, so now we have eliminated 'blowback' it seems to be after the mechanical pump, and before the injectors. I don't know what all this looks like. If there is a link to a diagram, it would be handy.
On these systems, any fuel that is pumped from the fuel tank to the injector pump but isn't used. simply returns to the tank - its a sort of continuous circulation system. Therefore, I guess the leak is on the return pipework just after the injection pump!
Its still on the low pressure side here.
Sorry for the late reply, John, I got confused by two threads in one.
I assume then the return might have a blockage that forces it to blow off.
We were a bit late to help, as it has been fixed by the seller, which is a welcome surprise.
Thanks all for your help.
Thanks for the replies