Yep, sounds like something cause the air/fuel mixture to be way off. Air leak at the manifold is the first place I would look too.
Agreeing with Fishpro and Lucky...
I have an 82 shovel that just had the same problems. Put new plugs in did not help, checkedfuel system top to bottom (carb intake petcock tank etc.) Still no help. I have a points ignition and guess what the dam backing plate came loose re set the timing and wala it ran idle was rough and would break up when cold. Only thing left was the coil replaced it and the engine has never run so good. I say check the ignition and the coil if you have an electronic ignition it usually has two circuits a start circuit and a run circuit. If you have points check the gap and the contacts for arc wear and if still no go replace the coil even they go bad every 25 years or so. Good luck
first thing i would do is check for air leak also the best site for ironheads is XLFORUM.NET got tones of good stuff but beware if you post a question the very first thing they will tell you is to get a factory service manual.
be sure the enrichener isnt stuck, and in automotive, i check for vacumn leaks is with the vehicle running i spray carb cleaner around the seals and gaskets, a leak will cause the motor to either rev a little or die when you hit it, but for whatever reason, it sounds like the plugs are fouled, back to too much fuel possibly, is your oil level way up? if so, float isn't working right, cylinders flooded out, change the oil if it smells like fuel, make sure the needle is sealing in the seat.
Not to sound too obvious but check the choke. If the choke was left on too long you fouled the plugs.
Choke ...points... wow brings back memories & nightmares.
Hey Pirate, ever get this figured out???
