How to Break in a RC Plane Engine

Like any combustion engines used in automobiles, motorcycles and lawn equipment, nitro gas-powered radio-controlled airplane engines need to have a break-in procedure done to them in order to properly "wear" the internal parts before regular use. This break-in process will assure that the engine will operate and seal correctly for the rest of its running life. If you start flying your RC airplane "all out" without breaking in the engine first, you will inhibit the engine's power potential or life expectancy. 

Dynam Pitts Model 12 Typhoon

Check with your specific model airplane engine's documentation for the recommended glow fuel grade for the break-in procedure. Model airplane fuel comes in three basic nitromethane grades: 10%, 15% and 20%.Decide how to break-in your model airplane engine. If the engine used for your airplane is already installed in the plane, break the engine in with it mounted to the fuselage. If you have not installed the engine in your model airplane, securely mount it to a workbench and hook it up to your fuel tank. 
Remove the wing of the model airplane and fill the fuel tank with glow fuel. Refer to your engine's operation manual to check for proper needle valve adjustment. The needle valve is the small thumb dial protruding from the carburetor and must be set so the engine will run "rich". 
Running the engine rich simply means increasing the concentration of fuel to air mixing within the carburetor. Screw the needle valve in all the way and then unscrew it to the proper amount of turns as dictated by your engine's operation manual. A rich needle valve adjustment will be 3 and 1/2 to 4 turns from screwed in position, according to www. rctophobby. com. 
Attach the glow starter to the glow plug, located on the top of the engine. Place the electric starter hub on the propeller cone and engage the electric motor to start the RC engine. Once the engine starts and runs steadily, vary the throttle from 1/4 to 1/3 of its maximum and occasionally rev the engine to half throttle. Shut off the engine after a couple minutes to allow for cooling time. Carefully place your thumb over the venturi opening, blocking the air intake to stop the engine. 
Be sure to keep your fingers away from the spinning propeller when performing this step. Start the engine back up after it has had enough time to cool down. Let it run for a couple minutes longer than before and continue varying the throttle. Repeat the cool down and running process until you have successfully used at least four tanks of fuel. Readjust the needle valve to the proper run setting outlined by the engine's operation manual. 

Nine Eagles 770B

Do this to keep your engine running smoothly and operating at the correct temperature. Perform a "pinch test" to determine the correct needle valve adjustments needed. Run the engine at full throttle and pinch the fuel line for one second; if the engine dies abruptly, then the fuel mixture is too "lean". A lean fuel setting means that there is a lesser concentration of fuel being mixed with the air inside the carburetor. 
A rich condition will cause the engine to speed up after you release the fuel line, a correct setting will indicate a slight speed up in engine speed when the fuel line is pinched and a drop of engine speed immediately after you let go of the fuel line.