1WildRT said

You spelled out most of what likely happened but missed the bigger picture... The headlights drew enough power to cause the point of high resistance (probably the bulkhead connector) to momentarily go open.. Thats what cut the ignition but the engine was still turning so air was still passing through the carb which caused the exhaust to get loaded with fuel, when the circuit closed & the engine fired again it lit the fuel in the exhaust...

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