Fuel Tank - Two (2) Lines or Three (3) ? What's the third fuel line for?

Question: My VMAR ARF model came with a three (3) line fuel tank stopper. What is the third line for?

Answer: The third line is a fuel fill line that allows you to fill the fuel tank without using the line that normally supplies fuel to the carburetor.

More Information: With a two line system, one fuel line supplies fuel from the fuel tank to the carburetor and the other line normally supplies muffler pressure to the fuel tank. When adding fuel to the tank, since there is a clunk on the fuel end of the line running to the carburetor, filling must take place through this fuel supply line which necessitates removing the line from the carburetor fuel nipple. This is a nuisance and can result in a split at the end of line when done many times. Such splits can result in leakage and difficulty in setting a reliable mixture setting.

By adding a third line, the fuel line that supplies fuel to the carburetor can be left in place during fueling. Fuel is added to the fuel tank through the fuel fill line (i.e. the third line).

After fueling close the fuel fill line off with a plug to allow the muffler pressure line to pressurize the fuel tank.

Note: Most engine manufacturers stress the importance of NOT flooding the engine with fuel during the fueling process. If you flood the engine with fuel and then try to turn it over with an electric starter you can severely damage any or all of the following components; piston, wrist pin, connecting rod, crank pin. This will not be covered by warranty and will necessitate a very expensive repair. The best way to avoid this is to ALWAYS do the following:

  • Remove the pressure line from the muffler during fueling
  • Turn the engine over by hand without glow plug or spark plug power. Rotate the engine through a full 360 degrees by hand before using an electric starter. If you cannot rotate the engine by hand, do NOT use an electric starter. Drain excess fuel from the cylinder and try again.