Many thanks guys for the thoughts.
Some answers to questions raised:
The hot starting is whilst on the ground! Typically I warm the engine up, kill it, set-up, restart and go flying. If I have to abort the take-off and kill the engine, then it typically won't re-fire for 5 - 10 minutes (frustraiting)!
"Where abouts are you?" Wells - Somerset
"i found it was the air filter" - The PAP only has an empty air box, no filter.
"pop-off pressure" - Now that is something I have not checked. Thanks for the web-link.
I did service the carb last Xmas, and she ran fine for months afterwards (not many hours because of the crap weather!).
What causes the pop-off preasure to "go off"?
Rob