Engine will run at times and not at others. No spark when not starting. Coil connections cleaned and sealed. Stator tests 11 volts. Books says it should be 18 - 20. Is that low voltage the most likely cause of the irratic starting? Magnets were glued in by somone else. Tach will not work. Regulator/rectifier is new. Power pack is 2.5 years old. Carbs rebuilt this summer. Fuel on plugs when there is no fire.