I think I see more spitback in the left carb. Could think of this as the right side exhaust has better geometries. Changing left exhaust length to match may be considered.
One test would be to disable spark on one side, then test ride on one cylinder.
Then, reverse the test, and compare...
One test would be to disable spark on one side, then test ride on one cylinder.
Then, reverse the test, and compare...