Furnace clean and tune. Cycled system. Checked heat exchanger, ok. Checked, removed, and cleaned burners and flame sensor. Both ok. Checked igniter, ok. Checked and tightened electrical connections and clamps. Clear drain lines. Checked and cleared pressure switch tubes. Checked and adjusted gas pressures to maximize efficiency. Preformed combustion test and found normal levels in exhaust. No CO found in airstream. System is currently operating normal at this time. Job complete.