Recently while dismantling my carbs (NC30) for cleaning, I was just doing the last carb(No4) when I got distracted by someone in the house. I left the pilot jet just sitting in its holder unscrewed and went off to see to the screaming daughter. When I got back having completely forgotten about the loose jet, I bolted up the bowl & reinserted the carbs. The bike ran horribly & on three cylinders. After a few minutes a load of black oil/petrol was spat out the exhaust in a pool. I immediately stopped the bike and restripped it where I found the loose jet inside the bowl. I replaced the carbs and put a newish plug in the No4 cause the one in it looked sodden & probably knackered ( they were only new plugs). When I refired the bike she was as sweet as a nut. My question is where did the oil come from, and there was quite a bit, I can understand petrol but not the oil?

Are you sure it was oil.. it could be a combination of petrol, soot and condensation which would form a thick oil like substance.

It certainly looked like oil, had the right texture, and where it hit the ground, I now have "Rainbow" type puddles, if you know what I mean.