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Gas Engine Basics

Gas Engine Basics

When you’re starting your gas engine, get into the habit of using the same procedure all the time so you can easily identify any problems that pop up. It’s important to always have a friend secure the airplane’s tail and make certain the prop bolts are tight. Switch the ignition circuit (kill switch) off, close the choke, and flip the prop a few times until the fuel begins to flow to the carburetor. Open the throttle fully, turn on the ignition switch but keep the choke closed. Flip the prop several times until you hear the engine “cough” or rumble telling you the engine is ready to start. Open the choke, reduce the throttle to a few clicks above idle, and then flip the prop again until the engine starts. The engine should fire up on the third or fourth try. Be sure to wear a thick leather glove for protection.


  • If your engine starts, burns off the prime then quickly dies, this indicates a fuel-draw issue. Check your fuel lines for any kinks, blockages or pin holes, and check your tank for proper internal setup.
  • If the carburetor won’t draw any fuel, check to make sure the needle valves are open. Also, check to make sure the carburetor is tightly fastened in place and that the small hole and passage feeding pulse pressure from the engine case to the carburetor isn’t blocked. Check the fuel intake screen filter and make sure it is clean. The screen is located under the top carburetor cap (the one held in place with a single screw). If it’s dirty, carefully remove it and flush it with fresh gas until it is clean. Finally, check that the engine head/cylinder case is tightly fastened to the engine case and that the gasket is undamaged. Even a small air leak here can prevent the engine from starting.
  • If there is no spark, check to make sure the kill switch is in the correct position. With electronic ignitions, make sure the battery if fully charged and the wiring to the timing sensor is properly connected.
  • If your engine loses compression, check for a stuck or broken piston ring. If this happens suddenly during flight, don’t turn the engine over by hand as this could score or gouge the sleeve. Carefully disassemble the engine and check for internal damage. If you don’t want to do it yourself, send the engine in for inspection and repair.
Updated: January 7, 2016 — 8:58 AM


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  1. Another cause of engine not drawing fuel is because the diaphram in the carb has dried and gotten hard……this keeps the carb from deawing fuel. Engine runs on prime then stops.
    This occurs in areas that have methenal in the gas….especialy if a jarge amount of time berween flying sessions.

  2. Good advise specially the habit or make a checklist of what to do.
    I was in the Air Force as a Crew Chief on F-15’s and F-16’s and we had an engine run checklist i never had a problem i couldnt handle and i would compare with other mech’s just to keep informed.


  3. Good advice! Just like propping a full-scale recip. And don’t forget – fresh fuel in the tank!


  4. Gas engines are the easiest of all powerplants to start and adjust! But with all things with propellers, be safe and have a friend available to secure the model’s tail while starting and if it is the first test run, to help you identify any possible issues. The best place to notice an engine performance issue is on the ground, not in the air. The plane you save may be your own. Have fun!

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