250-500cc WR 250 - wont start when hot

Hi all. My first race on my beauty (2008 WR 250) was yesterday. She was amazing and I'm so happy with her, but.... if I stalled or cut the engine in the pits it would not start without pulling the plug and kicking the bike over a few times with the petrol tap off. Not ideal in a race!. The plug was not wet and it was Brown to black'ish black'ish colour. When running it was 100%. I'm a novice level rider and it was a tight track so I couldn't ring its nuts off to clear it..

With all that info has anyone got an idea what might be the cause of the lack of starting?.. forgot to say once the plug was pulled as above it would start first kick..

I've not checked the wadding yet either so do not know if that is full of oil.

Many thanks as always

Myles