Model Engine Company of America
Instructions for
MECOA Engines

Do not attempt to fly your model before completely checking out your installation.

We stress the use of a chicken stick or electric starter to prevent injury when starting your engine. Do not use your fingers.

Keep your hands a safe distance from the propeller when making adjustments to the carburetor and when disconnecting the glow plug wire.

In case of difficulty, the safest and easiest way to stop the engine is to pinch off the fuel line or remove it from the carburetor. Never throw anything into the propeller (rags, etc.) to stop the engine.

Extreme care must be taken to protect your face, hands and body from the plane of the propeller. Don't start your engine on loose dirt, sand or gravel. A thrown blade or foreign objects drawn into the propeller could cause serious injury.

Never lean over the propeller and wear eye protection when starting and running your engine. Keep all loose articles (pencils, eyeglasses, etc.) out of shirt pockets, as they may fall out while adjusting your engine. Long hair, neck ties, loose shirt sleeves etc. must be kept away from the prop.

Never clamp your engine in a vice to test run. Mount your engine securely in your airplane or a commercial test stand. Never use wood screws to mount your engine. Use good quality machine screws and nuts.

Never run your engine in an enclosed area. Engines produce dangerous exhaust gases and must be run outdoors only.

Never use propellers with nicks, scratches or cracks. Always use the correct size propeller for your engine. Be sure prop nut is tight and recheck it after each flight. Nylon props can be extremely dangerous if improperly used. Read prop manufacturers directions carefully.

Never operate any model aircraft near overhead electric or telephone lines. If your plane should get away from you and become caught in overhead lines, DO NOT ATTEMPT TO RETRIEVE IT! Call the telephone or electric company and they will be happy to retrieve it for you.

Store your fuel in a tightly sealed container (metal or suitable plastic, NOT GLASS). Model fuel is poisonous and flammable. Keep it away from heat, flames, and the reach of children.

Use a muffler and fly in designated areas. Be considerate to others.

YOUR ENGINE IS NOT A TOY! It is a precision piece of machinery and should be treated as such.

If you are in doubt about anything, it is best to call our factory. Asking your hobby dealer or an experienced modeler for assistance may be helpful, but may not provide you with correct information.


With simple care and common sense your engine will provide you years of trouble free service. This product does require mechanical ability and know-how to operate. You must be the judge of your own ability. YOU are the person who will control your model and engine in a safe manner and must assume all responsibility for your activity.


This manual is written for a wide range of modelers, some information may seem elementary, but needs to be learned by beginners.

  These engines are designed for beam type mounting. Securely mount the engine an hardwood mounts or firewall mount with a good quality motor mount. Be sure mounting surface is flat and parallel and all mounting holes line up, the crankcase could become distorted if screws or mounts are forced. We strongly advise against using a soft or rubber mount installation as our engines are correctly balanced and these mounts can cause excess vibrations from resonance frequencies. Do not use a back cover mounting plate as the screw bosses are not designed to take engine torque.

Fuel tank should be located as close to the engine as possible. The center line of the tank should be within 1/2 inch above or below the center of the carburetor. Use muffler pressure to the fuel tank.

  USE A R/C OR IDLE BAR LONG PLUG, 1.5 volt battery, quality propeller (refer to prop chart) and good commercial grade two cycle glow fuel with 5% nitro-methane (more helps in cold weather). Be sure the fuel contains the right percentage of oil (17-22%) and the fuels oil contains at least a 50-50 mix of castor oil. Not all synthetic oil. Keep fuel clean and filter it during fueling. Keep exposure to air to a minimum as methanol will absorb moisture rapidly.

  BREAK-IN FORMULA: 22% Degummed castor oil (BAKERS AA or equivalent), or Klotz oil, 5 to 10% nitro-methane, and the balance methanol.

AFTER BREAK-IN: The nitro-methane percentage may be increased to 15% if desired. LOW QUALITY FUELS CAN RUIN THE ENGINE IN A SHORT PERIOD OF TIME.







Normal Models

8x5 ~ 8x6

9x6 ~ 10x5

10-7 ~ 11-5

10-8 ~ 11-6

11- 8 ~ 12-7

  All MECOA engines are produced to the highest standards and inspected before leaving the factory, but they are not "BROKEN-IN" and will require approximately 45 minutes running before the full potential of the engine is realized. Break-in can be accomplished by airborne or bench running.

A model engine makes sounds that will tell you how it's performing. You'll have to listen very carefully for them, recognize their message, and make adjustments to the fuel control needle valves accordingly. The mixture of fuel and air is controlled by the amount of fuel metered by the needle valve.

RICH MIXTURE running is characterized by a slower, sometimes irregular, sputtering exhaust sound. The exhaust gas will be smoky and probably contain small droplets of oil. This condition is good for Break-in since the engine receives excess lubrication and runs cooler.

FOUR CYCLING is a rich type setting, but it is fast enough to pull the airplane. This is the setting you normally look for before launching the airplane because the engine will run leaner when airborne.

PEAKED OR TWO CYCLE. As the main needle is closed (clockwise), it reduces the amount of fuel mixed with the air drawn into the engine. At a specific point, which varies with each engine, air temperature, altitude and relative humidity, the exhaust note will change quickly into a smooth, powerful note. If the needle is closed further, the note will stay smooth, but will weaken. The peak occurs just at the break point from a rich setting and further leaning will ruin the engine. A lean setting raises the engine heat above the safe point, reduces lubrication, and destroys glow plugs due to high combustion temperature. This is very harmful to the engine and your investment. Learn to tune the engine before flying. Remember, a little rich is always preferred for long motor life.

High speed needle is knurled knob and idle mixture is adjusted by the screw located in the center of the moving barrel.


Open the carburetor barrel about halfway. Open the high speed needle valve about 3 turns. Choke the engine by placing your finger over the venturi and slowly turn the prop over three times counter clockwise. You should see fuel being drawn up the fuel line. If fuel is not drawn into the carburetor, open the main needle two more turns, unscrew the idle needle two turns and repeat the above. Connect the 1.5 volt battery to the glow plug and pull the prop through until you feel a bump before compression. Now the engine will start with your chicken stick or electric starter. Once the engine starts, open the carburetor to full throttle. At this time the engine should be running very rich. Slowly turn the main needle valve in and the engine should start speeding up. If it slows, dies or only starts with a brief bust of power and stops, the needle valve setting is too lean. Unscrew the needle 1 more turn and try again. If engine starts, runs slowly and briefly the mixture is too rich. Turn needle in 1/2 turn and restart.

IF THE ENGINE DOES NOT FIRE AT ALL, refer to the troubleshooting section in this text.

  High speed needle is knurled knob and idle mixture is adjusted by the screw located in the center of the moving barrel.

MECOA engines are fitted with a variable mixture carburetor which automatically alters both fuel and air mixtures as it's closed. Best and most reliable carburetor settings are obtained after engine break-in.

1> Start the engine and open the carburetor to the full open position, then adjust for peak R.P.M. with the main needle as previously described.

2> Close the carburetor barrel slowly until the lowest possible speed is reached without the engine stopping.

3> Go to full throttle after about 10 seconds of idling. If the engine gains speed slowly, the idle mixture is too rich. If the engine stops, the idle mixture is too lean. Turn the idle needle clockwise if mixture is too rich and counterclockwise if too lean.

The engine will accelerate from idle to full throttle smoothly and instantaneously when properly adjusted. The engine may not idle well at a low setting or accelerate as quickly until it is well broken in.

AIRBORNE BREAK-IN (also see "aircraft installation")
  1> BREAK-IN running should be done with the recommended propeller (see chart above) at a slightly rich setting. The needle valve should be set at a point just into this range from a four cycle setting. Fly the plane at maximum throttle for 2 minutes, then throttle back for approximately 30 seconds. Repeat this sequence until approximately 30 minutes of accumulated running time has been obtained. Additionally, certain maneuvers, such as "CUBAN EIGHT'S", that allow the engine to load and unload are recommended. AVOID PROLONGED CLIMBING MANEUVERS AT MAXIMUM THROTTLE.

2> After the first 30 minutes change to normal size prop and fly an additional 30 minutes. Continue to run the engine at a slightly rich four cycle setting and fly your normal pattern.

3> After the above break-in period, run the engine at a normal peak needle valve setting. This should be a little on the rich side because engines run leaner in the air. 5% - 15% nitro may be used.


The initial bench break-in period is also approximately 60 minutes (30 to 45 minutes bench and 30 minutes airborne). During this time, use the recommended break-in propeller and run the engine at a rich setting. It is best to run the engine for about 10 minutes, then allow it to cool. The heating and cooling aid break-in.

1> Start the engine and run it at a rich full throttle for about 1-1/2 minutes, then let it fast idle (about 3500 rpm's) for 30 seconds. Repeat this sequence for about 20 minutes of running time.

2> Increase the full open throttle time to about 3 minutes followed by a 30 second idling period. Do this for an additional for 20 minutes.

3> Install the engine in your aircraft. Using an normal size prop, proceed as described in step 2 of "AIRBORNE BREAK-IN".

  Generally most engine starting problems can be traced to bad glow plugs, weak starting batteries, or inadequate fuel systems.

  The glow plug when connected to a 1.5 volt battery should glow a bright orange. If the plug slightly glows the battery or plug should be replaced.

If the seal leaks around the center plug post, replace it.

The glow plug element should be examined after several flights. If the element is deformed or touching the side of the plug body, replace it. If the glow plug element is pitted or has a frosty look, the engine is running too lean and continued running will seriously harm the engine.

  The most frequent problems encountered with fuel systems are:

1> Improper fuel tank location. The center line of the carburetor should be located on the center line of the fuel tank. See illustration.

2> Fuel pick up in tank is not free.

3> Dirt or contaminates in the fuel, tank, lines, filter or carburetor.

4> Holes in the fuel line. The tear resistance of silicon tubing is very low and it's not uncommon to develop a hole where the fuel line is assembled over the edges of brass tubing. If the engine runs well on the first half of tank and then quits, it's almost always caused by a hole in the pick up line inside the tank. Look for bubbles in the fuel line, this is also a sign of holes.

  When you are finished flying for the day, run your engine dry by removing the fuel line at a moderate speed or allow the fuel tank to run dry. It is best to squirt some RJL AFTER RUN OIL in the carburetor, then flip the propeller about 10 to 20 times. This oil will keep castor based fuels from gumming and protect internal engine parts from rust and corrosion. When storing your model between flying sessions, it is best to wrap your engine in a rag or plastic to prevent dust, dirt and moisture from entering the engine. The engine should also be wrapped in a rag at the flying field between flights.

Check tightness of all screws regularly.

If dirt does enter the engine do not turn it over until it has been flushed out completely. Alcohol is recommended for this. DO NOT USE carburetor cleaner or chlorinated industrial solvents as they may attack the plastic parts of the engine. The following steps may be used as a disassembly/assemble guide: (see warranty)

1> Remove carburetor, muffler and glow plug.

2> Remove the back cover and cylinder head.

3> Flush engine out completely using alcohol or mild solvent.

4> Install back cover and head. Insert screws into head and tighten until they just touch the head. Then tighten them. Tighten the screws only slightly, repeating the sequence a number of times until the screws are tight.

5> Install the glow plug and carburetor.


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MECOA is a Registered Trademark of Model Engine Corp. of America
Registered U.S. Patent Office

No part may be reproduced without written permission from
MECOA -- P.O. Box 5 -- Sierra Madre, CA 91025 U.S.A.