The engine cranks over but there is no spark at either spark plug, I have replaced tha coil no change.

Hi,
If it has a single coil, it must be an opposed twin. Is the "This side Up" phrase on the windings visible? Also, try disconnecting the engine from the rest of the wiring harness by unplugging the wire to the right of the air cleaner, usually a white or yellow wire. This is the ignition ground and will separate the engine from the frame. Won't turn off without reconnecting it, but it will steer you to the correct part of the machine.
Peace,
Clarke