Check your coil stick... I had the same thing once... with bike off... pull off the bottom plug cap from one side then see if the bike starts... then try the other side.
suggest you try some posh petrol out last saturday 1100 gs 1200gs and new kawasaki er6f no doubt about all bikes ran better. it is a little more expensive but i am told it contains unicorn tears (also found in the oil you have to put in a 1200gs)