Put a new fuel filter on when we serviced it about two months ago, so don't think it will be that, but could be something to do with the pump i suppose.
got a new dizzy coming now, so we'll see if that makes a difference.
Will be interesting to see if the new dizzy sorts it out for you, ill keep me fingers crossed!
Just as a matter of interest, has yours ever cut out? How long has it not been starting when its warm?