Inverted issues

Model Airplane News - RC Airplane News | Inverted issues

Clarence,     I have a OS BGX-1 mounted inverted in a one-fifth scale Pica P-40. I am using a J-Tec muffler.This engine is very hard to start. I usually have to turn the plane over, place in a cradle, then it starts, by hand, easily. I then shut it down, put the plane back on its wheels and quickly start it (but not always).  I have tried various electric starters with no luck.  I previously had this engine mounted sideways in another plane and it always started easily by hand and ran fine. When I choke it, lots of fuel just runs out of carb. Suggestions? Would converting it to gas help?       Thank you,   Bill F.

Dear Bill,

Like I have said many. many times in the column, anytime you invert an engine you can expect starting and idle problems. The glow plug becomes a sump where the raw fuel collects, putting out the fire. It is very important that the glow plug burn bright orange and not dull red so that it can burn off the fuel. As your engine will start okay side mounted or upright, it rules out any engine problem and is just your starting technique. You are probably just not getting sufficient fuel into the engine due to running out the carburetor. Try leaving the starting battery disconnected and with your finger over the muffler tail pipe spin the engine for three or four seconds. Then connect the battery and hit the engine with the starter, It should fire up right away. Placing your finger over the muffler tail pipe pressurizes the fuel tank forcing fuel to the carburetor and on into the engine. Let me know how it goes.

Good flying,


Updated: May 22, 2011 — 5:17 PM


  1. i had the same problem with an os max 75, i found that the inverted engines carb is well below the tanks fuel line causing flooding so i inverted the tank too and made a longer snorkel tube for the muffler to reach the bottom of the tank which is now the top of the tank, also use nice hot glow plug to burn fuel, flooding stopped and i can start the plane up right just got to get it dialed in now , good luck

  2. I have the same problem with an evolution .52.
    First it was mounted sideways in an extra 300 and worked always fine both idle and high rpm. Now I mounted it downways in a Ripmax’s Bossanova and started having troubles to start it up. Even high rpm does not work properly: when I fly normal it reaches much less rpm than flying inverted. If I close the high needle to reach more rpms flying normal, it gets very hot and flying inverted, it sounds like going to break.
    By the moment, I just change the OS8 plug with an OS6 wich is hotter, let’s see if it goes better.

  3. Ken,
    The BGX starts most easily by a brisk backward flip, after priming.

  4. A well primed inverted engine with a hot, dry glowplug should start easily. What I do with mine is…..Step One- remove glowplug. Step Two- prime engine by spinning with electric starter for 2 or 3 seconds. Remember, glow plug is out so there is no chance of hydro-lock damage etc.
    Step three- re-install glow plug and start engine.
    I only have to do this for the initial start. Once engine is warm it starts normally.
    Happy Motoring!

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