Hi I have a oil fired forced air furnace, I just cleaned it it was past due,I cleaned the blower ,the gun I removed and replaced the nozzle and cleaned the soot off the gun itself ,replaced the filter that is inline from the tank and now it is runnig fine but it is smokeing ,really black thick smokwe out the stack,what and why??

You are running to rich. Readjust the burner. You might need more air OR less fuel.

I had a similar problem when I was extreamly low on oil

Are you sure the new nozzle was the right one?