[Caprimaniac]

Nic. I think your problem with coughing etc while cruising might be adressed to one or more of these:
- Carbs not synchronized
- To lean (spec if exhaust popping) - to small idle jets or not far out enough
- To lean on some of the cylinders due to plugged idle cuircuit. Can be cleaned out.
I've had alot of troubles as you describe, reason was the third above options. Easy to check by using your fingers on the headers. But be quick, or else you'll burn'em.

But first of all you might check your cam to see if all cylinders open equal amount (weared lobes or solid cam need adjustment).