Motorcycle Questions? Ask a Mechanic.
Hi and welcome to JustAnswer,Thank you for the question and your patience. Should you still need assistance for information purposes only...Initially, possibilities; ...either be an electrical/ignition issue (most likely) or a fuel/delivery concern (least likely).
Proposed preliminary checks (if have not been done) on the possibility of over/under-voltage, regulator/rectifier and/or stator issue. With a volt/multi-meter, determine the battery voltage when:
Additionally, try revving the Vulcan with the regulator temporarily disconnected.
Please post back results / observations of the above once tried.
Appreciate the update and very significant information.
With "...carburetor is dumping gas into the piston...", then the most likely suspect would be the fuel inlet needle valve failing to seal inlet port when the carb bowl is full and float has risen. Possibilities then are:
This would require that the carbs be pulled out, dis-assembled, all metal parts soaked in cleaning solution and cleaning to remove varnish like dried residue. In most instances, a special cleaning tool similar to the product shown HERE would be needed.
It may be to your advantage to consider a repair kit similar to the product shown HERE.
Perhaps the exploded parts diagram HERE may help shed additional insight.