Ken;

From the symptoms, it certainly doesn't sound like the center two jugs are contributing their fair share...(and you can further verify this by feeling the exhaust plumbing right as it exits the head...but obviously only right after starting and before everything gets so hot you cant touch anything...)
...the symptoms also point to an ignition problem in general terms...unplug wire at the plug and attach to a spare plug laying on the grounded valve cover...check for spark at the plug...

also, check for spark loss at the cap, wires, or plugs (more easily located in darkness)

If it seems smooth at hi revs, thank your flywheel...but you should get it to idle smoothly too...

Good Hunting