first off, is there petrol in the tank?
Next up is why did you change the plug. Was it working before you changed it? Have you gapped the new plug to the appropriate sparking gap?
When the plug came out was it clean or burned or oily?
You can take the plug out and hold it by the insulated HT lead so that the threaded metal section of the plug touches a good earth (bare metal somewhere on your engine). Then when you press start/kick it over, if you see a spark all is well. If not then there's an electrical fault. Be careful not to get electrocuted here.
Do the lights and horn still work or is the battery dead?
Kill switch definitely in the right position?
