Black smoke on start-up

[chevychic]

Hey all,

For the last 3 weeks my truck has been blowing black smoke when I start it. It's just when I start it and not while idling or driving. I adjusted the carb over the weekend and I know I have it adjusted correctly. It was running a little rich before. I just changed the plugs today to have a somewhat fresh start with the newly adjusted carb.

It doesn't matter how warm the engine is, in fact, when it's cold, I don't notice any black smoke. But it doesn't happen ALL the time. Maybe 80% of the times I start it when it's warm.
Also when it does have black smoke, it's really stinky. It doesn't smell rich. It smells like something else is going on. The smell is kind of hard to explain. I guess the closest I can come is it smells like old burning grease. Not quite as bad as hot differential fluid but kind of similar...I think??

Another thing that might be worth noting is I have oil that comes out of the filler hole. I've replaced the PCV valve and checked the new one to make sure it was good and checked the breather hose for obstructions but all is clear.

Overall, it drives really good and has been very reliable lately. I just want to catch this problem before it gets worse and leaves me stranded someday....

Any clues?