It is necessary that a suitable oil should be used for lubricating the cylinder, and unless such an oil be used for this purpose the engine may run badly and perhaps stop altogether. Under no circumstances must a thick cylinder oil be used, and the oil must not be used over again on the piston. Do not use ordinary lubricating oil. A high-grade gas-engine oil especially suited to this engine should be used and the piston should be kept flooded with it. =Starting the engine.=—Throw the hand lever to “To start.” Turn the small crutch-handle regulator Y to the position “Shut” and work the pump lever up and down until oil is seen to pass the overflow freely. Turn the regulator back to “Open,” work the pump lever up and down a few strokes. Vapor should issue with some force from the relief cock on the cylinder. This indicates sufficient heat. Close the relief cock and pump a few strokes. Man the flywheel and start the flywheel backward, using the weight of the body if necessary, bringing the piston up against compression as sharply as possible, and then release the wheel, when an explosion should take place and the engine start forward. As soon as the engine has sufficient speed to carry it past a full compression, throw the lever to “To work.” When full speed is obtained, cut down the pump stroke to correspond to the load, open the oil feeders, and go over the engine carefully, seeing that the cylinder oil feed is working. =Oil pump.=—When the cylinder is working at its full power the distance between the round flanges on the pump plunger should be such that the hand gauge (supplied with the engine, and to be found in the tool box) will allow the part stamped “1” just to fit in between the flanges; if at any time the positions of these flanges be altered they can be readjusted to this gauge. The other lengths on the hand gauge are useful for adjusting the pump to economize oil. When running on a medium load, use length marked 2; on a light load, use length marked 3. See that the pump packing is not too tight. =Running the engine light.=—When the engine is to run light—that is, with no load or with a light load—it is best to alter the stroke of the pump to the amount of oil that will keep the engine running. This amount can be reduced so that the speed of the engine is a few revolutions under the normal, which will allow the vaporizer to get a small charge each time and keep it from cooling. The cock on the return of the water circulating pipe may be nearly closed to keep the cylinder warmer. These remarks do not apply when the load is intermittent and the engine is running light for a short time only. =Air-inlet and exhaust valves.=—See that the air-inlet and the exhaust valves are always working properly and drop onto their seats. They can at any time, if required, be made tight by grinding with a little flour of emery and oil.