I starting having the same problems with my 1987 xl 250. You can test the wire coming into your coil and leaving the coil with a electrical tester (the kind electrician´s use to see if wires are live). The coil itself is solid state and you can not do anything to fix it. If it is malfunctioning you will need to replace it. I made the mistake of buying the Honda part (over $80). You can buy an OEM coil for under $30. Having said all of that, I still continued to have problems with inconsistant spark. The motor has since siezed, the cam chain tore and the cam has been destroyed so I am replacing the motor with a CBX 250 motor instead. It will now have electic start and I am anticipating an end to my electrical issues as I have replaced the entire wiring system with the CBX system. I may have the only electric start 1987 Honda XL 250??? If anybody is curious about the motor swap and issues that I have encountered, let me know.