I recently installed Rinehart Racing 4" mufflers on my stock exhaust Road King.
When idling, I notice that the right side muff has much more flow than the left. When revved up, it's the same.
My V&H MO seemed to be balanced...possibly there was a bit of a restriction on the RH muffler to allow more pressure to the LH side.

Is this normal to have an unbalanced flow?

(these muffs sound AWESOME!)

 

Look at the header pipe under the bike...

You see that 'T' where it goes to the left muffler? Can you see how hard it is for the exhaust to flow through such an extreme bend as that? There is the reason. And, yes, it IS normal because of it's design. Maybe it's intentionally so, not sure, but I've heard that 2 into 1 headers are best for performance.

 

With the stock header, most of the exhaust will exit out the right side.