Glow Engine Adjustments by Douglas McLaren

Article put together from common knowledge by Douglas McLaren.

Top End:

Close needle valve, and then open 2 full turns. Ensure glow plug is in good condition and suitable for the engine. Start engine and run to full throttle. Slowly close the needle valve until the engine leans out. Pinch the fuel line gently between every adjustment to verify if RPM rises. If RPM rises, continue to lean engine. (Turn needle clockwise) When the engine is properly adjusted the RPM will increase a little if you gently pinch the fuel line. If the engine cuts when the fuel line is pinched – the engine is too lean. Finally – hold aircraft vertical in order to verify that the engine does not lean out and stop.

Bottom End:
Close slow running needle or screw (turn clockwise), and as in the former instance, open by approximately 2 – 3 turns. Start engine and run at full throttle for about 20 seconds. Bring engine to idle (around 2500 RPM approx.) and similarly allow to idle for about 20 seconds. Pinch fuel line to verify any change in RPM. If RPM increases and then stops – the bottom end is too rich (turn needle clockwise).

If RPM decreases and then stops – the bottom end is too lean (turn needle anticlockwise). To rectify – turn needle or screw about ¼ turn in the required direction and repeat process as detailed. The aim is to establish that the engine will not gain or lose RPM before stopping when the fuel line is pinched. When getting close to this ideal it will be necessary to make very small adjustments.

Footnote.
Run engine at full throttle and ensure that all is well, making any small adjustments that may be necessary. Ensure that the top end is properly adjusted before attempting to make any bottom end adjustments.