DIY Network

Gas-Powered Model-Airplane Engines -- Fine-Tuning Engine Speed From "Radio Control Hobbies" episode RCH-203

In this segment, Chris Chianelli and model-engine expert Randy Linsalato demonstrate the procedures in bench-tuning and break-in for a model engine.

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	Figure A
	Figure B
	Figure C
	Figure D
	Figure E
	Figure F

Fine-Tuning a 2-Stroke Engine

Important: This demonstration shows provides some of the basic information for operation of this particular model engine. There are variations in operation for each particular model. Read and carefully follow the manufacturer's instructions that come with yours, whether it is this particular model or another. Additional information about assembly as well as running, troubleshooting and fine-tuning the model can be found in the manufacturer's instructions.

Safety Alert: For testing and tuning an airplane engine, always be sure to wear eye protection. This procedure can be dangerous if not done properly since it involves the operation of powerful high-speed propellers. This procedure should only be done under adult supervision.

• For this demonstration, the gas-powered airplane engine is mounted on a test-stand made of machined metal (figure A). The stand is clamped to a heavy-duty table. Test-stands such as this are available through a number of hobby dealers.

• The engine used in this demonstration is a Model 61 from Mecoa -- an ABC engine. The engine has been fueled up, and there is a fuel-filter installed in the fuel line (figure B). The idle mixture -- for both low-speed and high-speed adjustments -- has been set to a rich-mixture setting.

  Safety Alert: Before starting the engine, make sure that you are not standing in the propeller's plane of rotation. Debris that inadvertently falls into the propeller can be thrown out at high speeds. Stand either in front of, or behind, the engine.

• The 1.5-volt igniter is attached to the glow-plug, and the engine is set to idle. Randy then applies the electric engine-starter (figure C) and fires up the engine. Droplets of fuel coming out of the exhaust are an indicator that the engine is running very rich at this point.

• With the engine at full-throttle, Randy adjusts the high-speed setting of the carburetor first. As the needle-valve is unscrewed (figure D), the engine slows down -- indicating a rich setting. The objective is to reach a high engine speed using the needle valve. (It's inadvisable to run an ABC engine at an extremely rich setting.)

• After an optimum high-speed adjustment is reached, then adjust the idle-speed mix to a slightly less-rich setting using a screwdriver (figures E and F) and re-start the engine. Repeat until an optimal idle speed is reached. A properly tuned idle speed allows for efficient acceleration.
  

It's important to note that these model engines are both air-cooled and liquid-cooled. The droplets of excess fuel and oil carried out through the exhaust are removing heat from the engine as it operates.

Important: When you're done testing or running a gas-powered engine, pull the fuel line from the carburetor and run the engine until it runs dry. Fuel alcohol left inside the engine will draw moisture into the engine and promote corrosion.

In the segment that follows, Chris and Randy adjust a 4-stroke gas engine.

Mecoa Engines

Crankshaft......hardened steel
Cylinder ...... hard chrome ABC
Carburetor...... all metal
Manufactured ...... USA
Street Price ?.. all ranges.