trecool44, How did you balance your carbs? What equipment did you use and the method?
I have my money on your issue rooted in a bad balance.
Some facts; the top plugs fire more efficiently because of their placement in the cylinder head. The front cylinders do not get the same mixture as the rear cylinders because of the longer intake manifold. I tell you this to help you understand why a carb imbalance can cause a differential mag drop. look at which plugs are responsible for the lower drop.
I had a very similar problem at 2500 RPM, a vibration and the left ignition had a much bigger drop than the right. This means the right ignition, coils, or plugs are the problem. After replacing the spark plugs, cutting back plug wires, swapping the ignition modules inputs & output plugs. It was traced to the only common denominator was the 2 coils and their related spark plugs.
Because of an unrelated issue I had to pull the prop and upon replacing it I did a dynamic balance and changed the floats to Marvel Schebler MS80-430, (got tired of the Rotax game). The last thing to do was a carb balance (which I was sure was fine). I ran the engine first to warm up and the problem still existed. After balancing the carbs it was all gone, vibration and difference in ignition drops.
MANY "experts" told me they thought my problem was fuel related, I was insistent it was electrical, I almost bought a coil pack, glad I didn't.
Live as if you were to die tomorrow. Learn as if you were to live forever.
-- Walt --