Troubleshooting Gas Engines

Troubleshooting Gas Engines

OK, so you’ve installed your gasoline engine properly, and made sure that the fuel tank is properly installed and the fuel lines and fuel filter are all hooked up correctly, but you still can’t get any fire in the hole—the engine just won’t start. As a safety note here, we always recommend using a properly sized heavy duty starter like those from Sullivan Products. If however, you are starting your engine by hand, be sure to have a friend help and hold the tail of your airplane secure so the plane won’t move forward when the engine does fire up.

What else can you do?

1. Well, the first thing is to check that the prop blade is positioned in relation to the magneto magnets or the electronic ignition’s triggering magnet as indicated in your engine’s operating manual. Sometimes a small adjustment in blade positioning will make all the difference.

2. I like to start my engines using my left hand and set the prop so that the blade is at 11 o’clock and I swing it to the 7 o’clock position. This directs the force downward instead of upward. The magneto fires the spark plug at about the 9:30.

3. If your engine starts, burns off the prime then quickly dies, this indicates a fuel draw issue. Check your fuel lines for any kinks, blockage or pin holes.

4. Also check your tank for proper internal setup. Sometimes, the fuel tank can be installed upside down, and won’t draw fuel properly. When you flip the prop with the choke closed, it should draw fuel. You can see it moving toward the carburetor in the fuel lines.

screen, walbro carburetor, RC, model airplanes, gas engines

5.  If the carburetor won’t draw any fuel, check to make sure the needle valves are open.

6. Also, 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.

7. Check the fuel intake screen filter and make sure it is clean. This screen is located under the carburetor’s top 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, or replace it.

8. 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.

9. If there’s no spark, make sure the kill switch is in the correct (Run) position. With electronic ignitions, make sure the battery is fully charged and the wiring to the timing sensor is properly connected.

10. 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, send the engine in for inspection and repair.


To ensure proper operation of your gasoline engine, always use clean, well filtered fuel. Use a filter in your fuel supply container, as well as between your engine and fuel tank. If you use a T-fitting in the engine supply line for filling and defueling your model, place the filter between the carburetor and the T Fitting.

Once set up properly and adjusted, gasoline engines are very user-friendly, start easily and provide excellent fuel economy. Once the carburetor is set, it won’t usually have to be adjusted for most if not all of the flying season.


  1. My Dle 30 normally runs great but during the last flight it just stopped dead in mid flight with a half tank remaining and all flight controls working. The ignition battery is fine. Can ignition just cut out some times? Thanks for any help.

    1. Hi Jay, it sounds like an ignition problem. My guess would be the kill switch. Check the wiring.Take the spark plug out and connect to the plug boot. Hold the plug against the cylinder head and give the prop a spin. You should see a spark when the magnet and sensor align. If not, then check the wiring, especially the ground. Hope this helps.

  2. I have a Saito FG-40 and using a starter it will fire intermittently but not start. Choking it I see and hear that it draws fuel, and since it fires (sort of) I would think that the ignition and spark plug is working?
    I’m quite new to gas engines (all other planes are electric), and would really appreciate anything to help solve this.

Comments are closed.

Air Age Media ©
WordPress Lightbox