Motorcycle Repair: spitting, backfire cold / fine warm, dyna lowrider, meter check

Question
QUESTION: I have a 2003 Dyna Lowrider.  V & H straight shots, go tthe performance air kit, the carb was jetted. I purchased the bike brand new in '03.  up until recently, it has been running great, before the pipes and after.  Now what i am experiencing is intermittently when the bike is cold, it will spit sputter and backfire like crazy, hard to run.  However, after i run the bike for about five minutes/couple of miles, it runs fine.  When i first pulled the plugs they were black, i replaced the plugs and it ran fine for several rides and now again black.  I took the bike to a local HD dealership and explained the situation to them.  after several days they called back to say that they AGAIN changed the plugs.  they told me it was because i was using the choke, i disagree and was a bit angry with the turn out, only because i have always used the choke in the same manner.  Anyway, i wanted to get your opinion on the matter.  this is the third plug change, something is fouling the plugs.  Plesae respond with detail, thanks

ANSWER: After riding the bike for a while are the plugs still black or just black when cold?
Mike

---------- FOLLOW-UP ----------

QUESTION: thanks for the quick response!  I pulled my plugs cold after riding back from the HD yesterday and the tips were brown and the rest black.  this evening i took it for a small two mile or shorter ride and the tips turned white and the rest were black.
ANSWER: I would do a OHMs test on the coil and plug wires to make sure they are good. If they pass, then I would check the carb to make sure the choke is not sticking open, even though you hae shut it off
Good luck and happy riding
Mike

---------- FOLLOW-UP ----------

QUESTION: can you provide instructions on how to test the coil? thanks

Answer
Remove the coil. With an OHM meter check from the hot wire to the rear wire (where the 12 volt wire goes) The do the same for the front. You should be getting .5-.7 Then test where the plug wires go. You should get 5,500-7,500 If it is not in range then it needs replaced
Good luck and happy riding
Mike