Furnace safety inspection. Cycled system. Checked heat exchanger. Found some rust and corrosion, but no cracks found with powder test and camera check. Found burners very rusted and corroded. Checked and cleaned flame sensor. Ok. Checked igniter. Ohmed and tested ok. Checked and adjusted gas pressures to maximize efficiency. Checked electrical connections and clamps. Found clamp on exhaust venting. Tightened clamp. Checked levels of CO and XS air in exhaust. XS air found to be 162. This is higher than desired. This is caused by a probable secondary partial blockage. This will continue to get worse over the next few years. CO was 13. This is within normal range. No CO found in airstream. This system is in need of a maintenance. Other than normal wear and usage, system is operating normal at this time. Yearly maintenance is recommended. Job complete.