Furnace clean and tune. Cycled system. Checked heat exchanger, ok. Checked, removed, and cleaned burners and flame sensor. Both ok. Igniter tested ok. Checked and adjusted gas pressures to maximize efficiency. Checked and tightened electrical connections and clamps. Cleared drain lines. Preformed combustion test and found normal levels found. O CO found in airstream. System operating normal at this time. Job complete.