Well, started it tonight and it idled steady at around 1,300 RPM, I touched the accelerator and idle was good, at times the idle rose to around 1,500 RPM but still steady, when I gave the gas a short sharp "Tap" this seemed to bring it back down to around 1,300 RPM again.

So as I thought, surely it has to be a valve issue James? It's just strange that when I dismantle it and reassemble it works for a while, I may try some light oil on it once more to see if it will revive it.

Martin