01 Polaris 500 XC SP would run for about 1 hour then it would back fire, loose power, stop. Let it sit, it would start back up & run fine again for awhile & then back fire. Replaced the thermostat sensor, tested the thermostat, & burped the cooling system. Now I did not have any spark. Replaced plugs, coil, CDI box, and stator and same issue. 40 VAC at exciter coil 1.6VAC at pickup coil 5.8VAC at stator. Any ideas?