My piaggio 50 won't start?

The bike has been standing for some time, did have a spark but doesn't now. I have connected the car battery and it is turining over fine. I checked the back brake light bulb as someone said this was in the ignition circuit. That's OK. The key was broken off in the lock but I think I have bypassed this. I have read about kill switches and things but I don't seem to have one. I have fitted a new coil but still no spark. Any suggestions please?