well, if your spark plug analysis doesnt resolve the problem, recommend you check the level of your oil (which often on sputter bikes is on the high side cold) and drain a little with a siphon so that the oil level is in between the middle and lower level when hot.

 

Other then the plugs that came in mine off the show room floor I run Autolite 4164 for 86K plus miles. I change mine every10K like the manual recommends. They still look good when I take them out but for $2 each just cheap insurance. On any plug make sure you check or set the gap.

 

After changing the plugs still had the problem. Went to a dealership for a benefit run. Happens to be one of my favorites regarding parts and service. The parts guy, very sharp suggested changing the plug wires. Rode a couple hundred miles yesterday and the bike ran great. BTW, the wires I had on there were braided stainless and only had them a couple months. Looked cool but ended up giving them to a guy riding a Dyna and he could use them to replace his obviously in need of replacement long wire. Surely both did not go bad so will hopefully work for him.

 

6R12 standard HD plugs there only $3.95 ea. changed mine yesterday at 10,000 miles they look just like the new one's except for the sandy brown color saved the old one's for just in case I need to change out on the road somewhere.