Check the pet cock and slide needle clip position, should be in cinter position. check for fuel in the vacume line going from the carb to the petcock, if there is fuel in the line the petcock is bad and dumping raw fuel straight into the intake through the vacume line causing a rich condition and fouling the plug!
Mine does the same thing, I know the carb and petcock is good. I've gone though them, petcock was bad, carb float level off, pilot jet was clogged, filter under the float needle was dirty. It runs fine for a while and then it quits like you turn the key off. I've got a problem some where. I'm running through my service manual and checking the next logical culprit. I need to pull the plastic and start checking the electronics.... it sucks.
Maybe, maybe not. I killed my battery, put in a new one and it started going weak again.
Check your charging rate, it should be at least 13.80, the manual says 13.50 but, the stock regulators are not even that good. Mine put out 14.11 at high rpm, manual says it should be 15.50. I don't run WOT much so, the idle number means more and mine was 13.00 to 13.11 battery at 12.60. After a year of that it will kill a battery. My regulator has totally died and a replacement is coming. I hope the generator is ok, the old regulator wouldn't keep the bike running long enough to check it.... The coil checked out so, I sure hope mine is the regulator.