This discussion pops up about once a week and I've written this same information time and again. Auto parts stores today, even the high performance parts suppliers sell almost exclusively 'resistance wire' . This wire is designed to cut down or eliminate interference with delicate electronic devices found in today's cars, even race cars. The conductor is non metallic, in most cases a carbon impregnated thread and there is a thick shielding insulation around it. The kit supplied spark plug wire, and some you'll find at motorcycle and lawn mower shops are copper or at least metallic core (conductor) If you measure the resistance with a good ohm meter you'll easily see the difference between resistance wire and metallic conductor. Any resistance will reduce the high voltage current produced by the CDI and transfered to the spark plug. Some will tell you that the high performance resistance wire is better than solid (metallic) conductor wire because it is used on race car engines and airplanes and so on and so on. The fact remains, the higher the resistance, the lower the voltage to the plug. We are not running high performance ignition systems which are capable of producing hundreds of thousands of volts in our motorized bicycles. We have a small magneto/capacitive discharge ignition system that is nothing like those in automotive use today. Find and use a good metallic conductor wire. The more current you can get to the plug the better. Just heard that AutoZone carries 7mm copper conductor, silicone insulation wire in bulk, sold by the foot. Some stores do not have it but can be ordered from their warehouse. Find a good counterman and ask for it.
Tom