Troubleshooting your fuel system

Aug 29, 2012 7 Comments by

Properly installed, your fuel system will last a very long time and may never need to be changed. In a hard landing, however, some of its parts may be dislodged and stop working. Here are some common fuel-flow problems and fixes.

  • If your engine begins to run lean, check for small pinholes in the fuel-supply line. Check closely wherever here are tight bends in the line, or where it comes ino contact with your model. Leaks commonly occur where the lines pass through the firewall. A better method of installation is to drill small holes in the firewall and use lengths of brass tubes in the holes. You can then slip the fuel lines over the brass tubes to complete the system.
  • After a hard landing, the flexible pick-up tube and clunk inside the fuel tank may be forced all the way forward. This often goes unnoticed until the next flight, when the tank stops delivering fuel to the engine in a nose-high altitude. To prevent this, solder a short piece of brass tube to your clunk. This decreases the pick-up tube’s flexibility but still allows it to draw fuel in normal flying attitudes.

  • If your engine begins to run erratically, chances are that some debris has gotten into the fuel system and is blocking the carb. It usually finds its way into the fuel tank from your fuel jug, and if it blocks the fuel flow, your engine will die. The easiest way to prevent this is with an in-line fuel filter. You install it just before the carb in the supply line. You can also install a filter in your fuel-pump line so you can fill the tank only with filtered fuel. Add a combination fuel clunk/filter and you’ll have a triple defense against deadsticks.

These tips are excerpted from “RC Fuel Systems” in our FLIGHT READY book, available at the AirAgeStore.com. Order your copy today!

Debra Cleghorn, How-tos

About the author

Executive editor About me: I’m a publishing professional who has a passion for aviation and RC, and I love creating issues, books and a website that help RC pilots to enjoy this sport even more. I admire scale aircraft and enjoy the convenience of flying smaller electrics.

7 Responses to “Troubleshooting your fuel system”

  1. David says:

    Another problem with gas engines is ethanol reacting with water to form a gelatinous substance that clogs the carb screen. At first glance the screen may seem fine, but closer inspection will show the mesh uniformly coated with jelled fuel. This problem comes on suddenly in the form of dead-sticks and poor idle, and will probably effect all the fuel systems in your fleet that you have fueled from the same source. Cleaning the screens, dumping the bad fuel, and adding an ethanol fuel stabilizer solves the problem.

  2. Richard says:

    David, help us with the ethanol fuel stabilizer. Brand names and where to buy it.

    Thanks a bunch,
    Richard

  3. Mark Danemann says:

    I recently had an issue with an O.S. 72 four stroke that was educational. The engine ran fine but after it was warmed up, it wouldn’t start. When looking at the fuel line, the fuel wouldn’t quite make it to the carb. I checked the fuel system for leaks and for a blocked vent line but I knew there was pressure because it was coming out of the fueling line (I use a three line system). Ultimately the idle screw (or mixture control valve) was set a little lean so it wouldn’t let fuel in once the engine was warm. I made it a little richer (1/6th turn out) and then readjusted the needle valve to compensate (they work together) and not only would it restart every time but it ran better at full throttle. I wanted to share because I have never seen this behavior and the solution was ellusive as I rarely touch the mixture screw.

  4. josh says:

    ok. heres the issue im having. os 46axII w/ Bisson Pitts muffler. the needle valve was uneffective at anything over half throttle. no air leaks problem was fixed by plugging on the the muffler ports but i feel im losing power with this fix. ive seen reviews of the same setup w/ no mention of this issue. anyone have any suggestions?

  5. Tom Pomeroy says:

    Sounds like a restriction in your fuel delivery system that is starving it at hi rpm . Opening the needle doesn’t help because the restriction has become the max flow limiter.
    I had a smiler problem that turned out to be a partial restriction where the fuel nipple and spraybar were silver soldered together. Took me 12 years to figure it out.
    The engine would only turn large props (no rpm) to gulp fuel.
    A restriction like this could be anywhere upstream of the needle and just seeing some flow won’t proove it to be ok.
    I ended up using number drills until the ID of all the parts was at least the size of the sparybar bore…all the way thru.

  6. Tom Pomeroy says:

    similar not smiler….oops

  7. josh says:

    thanks Tom. i’ll look into that.

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