Pearl Harbor MAN 900x250
Log In
Access Premium Site»
Not a member? Join today!

Troubleshoot Gas Engines — 11 Tips for Reliable Performance

Troubleshoot Gas Engines — 11 Tips for Reliable Performance

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 personally 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.


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.

11. 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.

Updated: October 12, 2016 — 10:29 AM
Hobbico RF8 Get Real Giveaway 600x120
PhotoDrone 600x120


Add a Comment
  1. Sometime you go to the airfield and when you come back home (after a negotiate to have this afternoon) … “how was your flights this afternoon ?” … “well darling … I just turn my prop all afternoon to try to start … but believe me I learnd lot of things …(sic)” ahahaha

    1. Anytime I went to the field and could not fly for any reason, the good news was, I brought my airplane back undamaged and good for a better day. Lol.

      1. haha can we have an amen 😀

  2. Primary reason(s) for most “no starts” is (1) Old fuel with wrong oil mixture. (1) Electronic system is not firing based on bad magnet or bad timing (3) Fuel mixture screws have been “improperly” adjusted–check carb specific settings. (4)Small Electronic sensing devices are available to check both “magnetic” functions of sensor and shaft. (5)Also devices to insure the electronic “box” is providing adaquate spark. (6) Finally, the plug can cause a lot of problems. Make sure you are using the correct plug and the “spark plug boot” is securely placed around the spark plug hex portion of the plug. Check each item and don’t forget…”too many cooks spoil the broth”……..take it home and work!

  3. Where can we find the devices you mentioned for checking spark value and magnetic functions?

    1. spark testers are available at auto parts stores and lawn mower parts suppliers.some look like a spark plug with an alligator clip on the side.adjustable gap versions can give you an approximate voltage(in kilovolts)of your spark.

    2. Hobbyking have a tiny spark tester about the size and shape of those small pronged lipo testers it comes with a timing gauge as well

  4. One other thing I have found that can cause frustration, dry gaskets. On a brand new engine, like for example DLE 20, the carb gasket that pumps the fuel from the tank can be dry and not flex very well, and you wind up spinning all day trying to draw fuel. Take the gasket off, soak in in gas for 10 minutes, put it back on and you will get fuel. Same can happen on an engine that has sat for a long time, my DLE 30 was like that, took a long time to draw fuel, even with an electric starter, but now that I have a couple runs, it draws and starts on a few flips.

    1. @Todd:

      You brought up one of the most common problems of small gas engines with walbro and zama-type carburetors – The diaphragm. However, you called it a gasket. So, to set the record straight, it’s the DIAPHRAGM. It uses
      crankcase vacuum to draw the fuel from the tank. It also operates the metering needle which controls fuel flow into the carb. When the diaphragm dries out and stiffens, everything else can be perfect but the engine will refuse to start.

      1. I thought the rubber diaphragm was just for metering and the fibeglass looking diagphragm on the other side (the side with one screw holding the cover on) was actually the fuel pump?

  5. Yes!! I would like to know the same thing as Carl Stewart in his reply. But I really appreciate this article and all of the replies. This was “VERY” informative and helpful.

  6. Alot of great info, remember on a 2 stroke, if it’s getting fuel and spark it will fire, won’t fire without either

  7. Wow,all this trouble to go for a fly.Change to modern technology and go electric,problems solved

  8. I have a DLE 30 that I need to prime to get it to start for the initial start up.
    It’s difficult with the rear mounted carb, but after the first flight starting is easy, usually 1 or 2 flips of the prop and it’s up and running.

  9. Bill, I had the same problem with a 26cc that needed priming on the initial startup. I solved the problem by purchasing a priming pump for weedwakers or such at a small engine repair shop. I installed it on my model with the outlet fuel line ending with a piece of brass tubing aimed right into the motor’s air intake about one inch away from the intake. I depress the priming pump till it fills up with fuel and then another two shots for the actual prime. The motor usually starts after a few flips of the prop. Good luck.

  10. One thing all need to take into account at the end of the year for those using mineral based oil. Run the system dry, if you don’t the fuel evaporates and some oils will gel. This then dries to a hard and crusty problem and then the small fuel orifices ate plugged. Easy to do and I’ve not had problems ever.

Leave a Reply

Your email address will not be published. Required fields are marked *

Airage Media © 2017
WordPress Lightbox