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OS have released a few notes to help customers get the best from thier GT15HZ engine.

The most common issues are:
  1. Plug cap is not installed on the plug completely, which causes a RF noise issue. We have noticed the installation requires some force to fit properly.
  2. Piston skirt can be broken by using unsuitable tool including a wrong O.S. Crankshaft Clamp. OS offer a special Crankshaft Clamp to use with this engine (X-OS71530530).
  3. We have found many GT15HZ owners are new to gasoline engine. Many have made a mistake by setting the needle too lean, causing overheating and engine failure. Attached is an additional NOTE on the needle adjustment.

Please download these documents:
How to adjust the GT15HZ carburettor

Please watch the official setup video from OS.

The adjustment range of a gasoline engine’s carburettor is very narrow and the needle setting is very sensitive compared to a regular glow engine. A small mis-adjustment of needles often results in overheating and possible damage. The oil content of pre-mixed gasoline/oil fuel is also much less than glow fuel giving less tolerance to error. Adjust the needles following the procedures below.

  1. GT15HZ has two needles, High and Low.
    The left needle is for Low, Right needle is for High, with the engine being mounted in the helicopter. GT15 Needles
  2. Factory setting of the needles
    Low needle : 1 + 1/4 turns from the fully closed position
    High needle : 1 + 3/4 turns from the fully closed position
    Note : This factory setting is very important. Please make sure that both of the needles are at the factory positions before starting the engine for the first time.
  3. Starting the engine
    Start the engine following the instruction manual procedures. Choke and prime it to make the start easier. Excessive priming floods the carburettor and can cause piston locking (hydraulic) with potential damage to the connecting rod. Warming up after starting is necessary for gasoline engines, especially in cold winter weather. Continue the warm-up run for 1-2 minutes on the ground with the main rotor slowly rotating before attempting to raise the rotor RPM and fly.
  4. Take off after the warm-up run.
    When the helicopter takes off, adjust the needles according to the scenarios shown below.

    Scenario 1 - Low needle adjustment is rich
    When you open the throttle to take off, the engine RPM don’t increase with a lot of white smoke coming from the exhaust pipe.

    Solution → 
    Turn the Low needle very slightly (say 6 degrees) clockwise and try to take off again. Each adjustment should not be in excess of say 6 degrees. Gasoline engine carburettor needles are much more sensitive than glow.

    GT15 6 Degrees Clockwise

    Do not touch the High speed needle before completing Low needle adjustments.*

    If the situation doesn’t improve, repeat the adjustment increment clockwise as before. Continue the same process until you can take off normally. Once the helicopter takes off, you do not have to close the Low needle any more. Excessive needle adjustment causes over-revving and raises the potential for engine damage.

    Scenario 2 - When the Low needle is lean
    When the helicopter takes off, the engine runs at very high RPM (more than 1,500rpm at the main rotor), hesitates before picking up speed and smoke is low.

    Solution →
    Turn the Low needle, say 30 degrees in the counterclockwise direction.
    GT15 30 Degrees Counter-Clockwise

    Try to take off again. If the situation doesn’t improve, turn Low needle 18-30 degrees counterclockwise again. Repeat this process until the engine doesn’t over-rev as you rise into the hover.

    *As mentioned in the manual, we recommend lowering the throttle curve to prevent the engine from over-revving.
  5. Start running-in, which is vitally important for gasoline engines.
    After confirming stable hovering with the main rotor rotating at around 1,400 – 1,500rpm, start the running-in process, consuming 2-3 litres of fuel. * The further you continue running-in, the more happily the engine will run.
  6. Flying normally after running-in
    After switching the flight mode, climb away for normal forward flight. Adjust the High needle according to the scenarios below.

    Scenario 1) * When the High needle is rich *
    When the throttle is fully open, after switching the flight mode, the engine responds sluggishly to increase rpm and power.

    Solution →
    Turn the High needle clockwise very slightly (5 degrees maximum) or less. Each needle turn must be less than say 6 degrees because the High needle is more sensitive than Low needle.
    GT15 6 Degrees Clockwise

    * The maximum High needle turning adjustment must not exceed 30 degrees in total from the factory setting (1 + 3/4 turns from the fully closed position)
    GT15 30 Degrees Counter-Clockwise

    To lean the needles excessively causes overheating as gasoline engines create higher temperatures than glow engines.

    Scenario 2) * When the High needle is lean *
    When the throttle is fully open after switching the flight mode, the engine responds sluggishly to increase rpm/power and smoke diminishes. The engine may try to quit running as well.

    Solution → 
    Turn the High needle counterclockwise 30-60 degrees. 60 degrees of turn maybe too much, but rich running does no harm. Continue rich running for a while.

    A little turn of the High needle results in drastic change. Take your time to adjust it properly.
  7. Fuel flow during operation is very low.
    Gasoline engines have lower fuel consumption than glow engines because fuel flow during operation is very low. For this reason, the needle adjustment is very sensitive, but once the adjustment is set, it lasts longer. Please make the adjustments with patience, without turning the needles excessively each a time. If in doubt, always make a rich decision rather than a lean one, especially on hot days and flying sites at high altitude.
Here are important points to avoid engine failure due to overheating caused by lean setting.

  1. OIL
    Be sure to use an oil for the 25:1 mixture fuel with which you can hover the model with small adjustment of Slow Needle (Max closing : 45 degrees, 6 degrees at a time). So far, we have checked the following oils OK.
    • Zenoah Genuine FC Class
    • Klotz ModeLube
    • AMSOIL Saber
    Adjust with the throttle curve and slow needle so that rotor RPM at hovering may be less than 1,500. Note again max closing of the slow needle is 45 degrees.
    Never close the high needle more than 30 degrees.