My 2001 XR650L has a strange intermittent spark. When trying to start it, it fires once but won't run. Backfires like a freakin' cannon through the exhaust when it does fire. I pulled the plug and layed it against the cylinder head. When cranking the engine, the plug fires once when the start switch is engaged and does not spark while the engine spins over. When I let off the starter button, the plug fires once more. I swapped numerous plugs, no change. Unplugged CDI harness and checked connectors...clean and dry. Checked safety switches and kill switch, no problems there. Is this symtomatic of a bad CDI? Any ideas would be greatly appreciated....thanks!