Use sturdy engine mounts. Make sure that these mounts are firmly integrated with the airframe, reinforcing the internal surrounding structure as necessary to absorb vibration. Wobbly engine mounts will allow the engine to vibrate excessively and may damage the model and cause foaming of the fuel tank. Also, the fuel tank is should be located so that the center line of the tank is 10 to 15mm below the center line of the needle-valve in order to prevent "flooding" of the carburetor.

We recommend you always use a good quality hard wood propeller of the size shown:

Engine Size >>








Prop Size

7 x 6
8 x 6

8 x 6
9 x 6

9 x 6
10 x 6

10 x 7
11 x 6

11 x 7
12 x 6

11 x 8
12 x 7

14 x 8
16 x 6

We urge that you do not use nylon propellers because their flexible nature causes more vibration. Also, there is greater possibility of propeller fracturing and blade flying off. If a spinner is used, make sure that the spinner notches are large enough to clear the propeller blades and do not cut into and weaken the blade roots when the propeller nut is tightened.

WARNING: Always keep clear of the propeller when starting of adjusting the engine. Never throw anything into a running engine to stop it. Never alter, repair or share a propeller.


The carburetor of the GMS engine has been factory set for the approximate best result, but the settings may, in some cases, vary slightly in accordance with fuel and climatic conditions.

Three adjustable controls are provided on this carburetor:

1.  High Speed Needle: For adjusting the mixture strength when the throttle is fully open.

2.  Idle Needle: For adjusting the mixture strength at part-throttle and idling speeds, to obtain steady idling and smooth acceleration to full speeds.

3.  The Throttle Stop Screw: For establishing the minimum idling speed.


Model airplane fuels are a mixture of methanol, oil, and various additives to improve ignition, add power, and cut down carbon deposits. It is important to use fuel with a castor oil and/or synthetic lubricants, otherwise, your engine life will be drastically reduced. Nitro is another fuel ingredient that is often used. Its function is to "advance the spark". To determine if you need any, or more nitro, start your engine, open the throttle wide open and set your high speed needle for maximum power, then back it out slightly. Do all this with your booster battery connected. Now remove your booster leads - if your motor slows down, more nitro is indicated. Conversely, if your motor speeds up, there is probably too much nitro. We recommend high quality commercial fuel with 10~15% of nitro.

WARNING: Model airplane fuel is both flammable and extremely poisonous. Run your engine only in a well ventilated area.

  This series of engines all use the long thread glow plug. We recommend medium heat range plus.

1.  Mount your engine securely on a mount that does not put a strain on the mounting lug.  The fuel supply should be so positioned that the fuel level is no more than 1/2" above or below the fuel nipple. The fuel line should not be higher than the fuel level at any point.

2.  Close the throttle - adjust the idle stop screw, to approximate the diameter of a pin when the throttle is pulled close.

3.   Screw the high speed needle in until it seats, then back out approximately 1 and 1/2 turns.

4.   Set the throttle at 1/4 open throttle position and prime the engine by placing a finer over the air intake and flipping the propeller counterclockwise a few times. Now, connect the glow plug wire and crank counterclockwise with a quick, snappy, and flipping motion, or better, using an electric starter. It is preferable to have the throttle only slightly open, to avoid unnecessarily high revolutions when the engine starts.

5.   A good indication of whether you have your idle needle set correctly is that if your engine choked to stop when you apply the throttle from idle, it represents the mixture is too rich and you can turn the screw clockwise by 1/4 turn. On the other hand, if your engine speeds up very quickly and then stops, it is too lean and you should unscrew it by 1/4 turn.

WARNING: A model airplane engine can get hot enough to cause a serious burn. Do not touch the engine right after it has been run.

Your GMS engine has a closely fit piston which requires only 15 to 30 minutes running before it will idle reliably. No special fuel or propeller is necessary, but it is recommended you use the fuel and propeller you intend to use in your plane. Take care that the engine is not run overlean (leaned in to the point that it loses power).

NOTE: Make sure that the engine is fully "run-in" before operating it continuously at full power. Otherwise, the life and performance of the engine may be reduced.


The following can help to ensure long life and maximum performance from your engine:

1.   Avoid running the engine under dusty conditions.
2.   Use a fuel filter between fuel tank and carburetor.
3.   Do not leave fuel in the fuel tank at the end of a flying session.
4.   Always keep the exterior of the engine clean.
5.   If the engine is not to be used for a long time, remove the glow plug and rinse the interior with kerosene by rotating the crankshaft. Shake out the residue and then inject.

  When you use low nitro fuel, sometimes, if you start the engine by hand, you will feel it's quite hard to flip over the propeller; it's possible that the compression ratio is too high. If so, please add one or two pieces of cylinder gasket. On the contrary, if the engine can be started very easy but RPM is not high enough, it's possible that the compression ratio is too low. If so, please take out one or two pieces of cylinder gasket.


©2005/1997 Model Engine Corporation of America, All rights reserved.
GMS is a Trademark of Model Engine Corp. of America

No part may be reproduced without written permission from
MECOA -- P.O. Box 98 -- Sierra Madre, CA 91025 U.S.A.