Adjusting Your Needle Valve
(Or How to Ruin an Engine Real Fast)
by Jerry Kelly
Lean engine runs ruin more glow plug engines than anything I know of. Here is the traditional method for adjusting your needle valve for high speed.
1. Start the motor and screw the needle valve in (lean) until the motor is running as fast as it can run (when the motor slows up you have gone to far.)
2. Unscrew the needle to the point that it losses a little RPM..
3. Now raise the nose of the airplane to a vertical position. The motor should speed up because it is drawing fuel from several inches lower than when in the normal position. If it continues to run at the higher speed without sagging (give it plenty of time) lower the plane to the normal position. It should go rich again, if not open the N. V. a little and try again until it runs fast and steady in the vertical position and slows when returned to normal.
4. The set up should be good for a test flight. If the motor does not lean out during the flight you can go lean a click or two and make another flight. Every flight should be observed to adjust for the next flight. If the motor runs fine, leave it alone. If too lean or too rich, adjust a click or two until it is satisfactory.
5. Play it safe and keep on the rich side and the motor will last for many hours. A couple of lean runs and you’ll be looking for another motor.
6. This does not apply to engines with tuned pipes