Paul, i have trouble firing the 500 up when its cold all last season till recently, takes a lot of kicks. i found that pulling the plug out and spraying "Start ya Bastard" down the plug hole (or even a bit of fuel will do) it then fires in 2 kicks.
after that its first or second kick every time. i think the problem is getting an initial charge into the pot to get them to fire, try it and let me know how ya go.