Your problem sounds like ignition to me, and I can only think of two things that could cause this: The coil or the igniter--I would replace the coil first since it costs much less.
You mentioned checking the fuel filters--did you check the small inline filter in the top of the "T" connection between the carbs. The fuel line goes from the petcock to the "T" and then to each carb--the small screen filter is inside the "T" connection.
Larry
You mentioned checking the fuel filters--did you check the small inline filter in the top of the "T" connection between the carbs. The fuel line goes from the petcock to the "T" and then to each carb--the small screen filter is inside the "T" connection.
Larry