beside the fact that to read the plug properly you need to put new plugs in give it a hard run somewere safe and turn the ignition of at full noise to get a proper reading. if you have your breather pipe conected to the inlet under full noise it will throw oil into the intake, hence the use of catch cans. some of the unleaded fuels and additives do leave deposit on plus and depending on modes you might need a hotter plug. its prob just a bit of oil thrown into the intake from the top end but if you want to check go some were safe and put a new set in and give it a hard blast and turn it of at full noise and roll to a stop,pull plugs out and smell them and look. this tell you if to much fuel in one etc.
mick
p.s hi stew, pm me for my new number