Thanks for the advice – might be worth trying Hayter first. If no joy with them I will try cleaning the carb. Will try and find a vid online of how to do that, I have the bad feeling that I will try and springs will fly out everywhere then I’ll have to just throw it away :-(
It’s relatively new, I bought it last year but can’t easily get back to the shop so would have to try Hayter direct.
The temperature comment is interesting – that’s exactly what happens. Turning engine off and back on doesn’t affect it at all, just time, so temperature related is likely.