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69.     Airplane Motors.

reduced. Never drop spark plugs, because there is danger of cracking the porcelain; and always shake them to see if you hear any rattle in the porcelain. Unfortunately there is often no way in which we can detect the crack in the plug unless it is by noting that the spark fails to burn the points white or that the cylinder misses at high speed. It is an excellent plan to put a few drops of oil on the spark-plug thread before screwing it into the cylinder. If you ever have one stick in a cylinder you will never fail to do this.

Lecture VII.

Inspection or "Prevention" of Trouble.

1. In airplane-motor work if the motor fails the aviator usually fails to accomplish whatever he started out to do. This means that it is important to prevent trouble by means of careful planning, thorough inspection, and forethought, rather than to wait until the trouble occurs and then figure out a way to fix it. Inspect in a systematic way. Begin by inspecting the gas feed. To do this, first examine the gas tank and see that there is a good air vent and see that the air vent is not plugged up, because gasoline will not flow from the tank very long unless air can get in to take the place of the gasoline. Next, test the flow from the pipe where it connects with the carburetor. Clean the settlers and strainers in the gasoline line. Clean the carburetor thoroughly, including the jets. Then examine the intake manifolds for air leaks or loose joints. It is important to examine the throttle controls. The best way is to have someone sit in the pilot's seat and operate the throttle, then stand where you can see the carburetor and be sure that when he operates the throttle that it opens all the way and be very sure that when he closes the throttle it closes closes all the way. This is exceedingly important because it is quite possible to install a new motor or carburetor in a machine and the throttle controls may not fit. The result may be that the throttle will not come anywhere near closing. Then when the