Upon arrival furnace was off on reset. Pressed reset button and furnace lit but was rumbling. Checked the oil flow and had great flow. Checked the nozzle and saw it had been dripping for some time and there was carbon buildup on the nozzle and beneath it. Replaced the nozzle and cleaned the carbon. Started and tested the furnace. Cycled it on and off multiple times to burn off all residual oil. Performed combustion test. Unit is running at 8.4%o2 60ppm co 0 smoke