Figure 4-57. - Setting of ignition points and nozzle.

thermometer halfway between the center and outside of the smoke pipe and not more than 12 inches from the furnace between the smoke pipe connection and the draft regulator or barometric damper. Be careful to prevent the thermometer from being influenced by cold air taken in by the draft regulator.

The flue-gas analyzer is used to determine the percentage of CO₂ produced by combustion. The CO₂ reading shows how much excess air is being used. Along with the stack temperature, it denotes the efficiency of the furnace. If, despite a good flame setting, CO₂ readings are low, examine the furnace for air leaks.

FUEL PUMP

Maintenance requirements include cleaning the strainer, servicing the valve seat and needle valve, and adjusting the pressure regulator. Strainers must be cleaned frequently to prevent the screen from clogging and causing a shutdown. A good test for valve operation consists of removing the nozzle line at the pump connection, starting and stopping the pump, and observing whether the valve cuts off sharp and lean. When necessary, the valve is easily serviced by removing the valve chamber cover, holding spring, washer, adjusting spring, cap, and bellows assembly. Then, by taking off the nut that is marked "Nozzle," the valve, valve guide, and plug assembly can be removed.

Adjustment of the pressure regulator can be done by replacing the vent plug with a pressure gauge, removing the cover screw, and using an Allen wrench to turn the adjusting screw clockwise to increase the pressure or counterclockwise to decrease the pressure.

Burner failure or improper unit operation can be caused by various problems. Often the problem can be pinpointed by observing the type of failure and giving it some thought before attacking the problem. At other times, the cause can only be determined by a process of elimination. Table M in appendix II lists specific oil pump troubleshooting procedures, while table K, also in appendix II, lists general oil burner troubleshooting 4-37