RCU Forums - Engine tune

Patrick,

Verify break-in was done according to this thread:

http://www.rcuniverse.com/showthread...59&forumid=145

Verify your fuel lines are as short as possible, but the clunk still reaches within 1/8" off the rear of the tank. It must be insulated from direct contact with any part of the airframe, by 1/4" foam latex, to prevent vibration and foaming.

Verify it is installed within 1/4" above, or below the carburettor spray-bar.

To adjust the engine, start with a rich main needle setting and with the air-bleed screw covering one half of the air-bleed orifice.

Set the throttle to full speed and lift the plane's nose straight up.
It is preferable that someone will hold the plane firmly, while you adjust.

Close the needle gradually until closing further doesn't add speed, or causes a loss thereof. Then open the needle back until speed is 100-150 RPM below maximum. That would do for the main needle.

Now set the plane on its landing gear and close the throttle to idle position (about 1mm open).
Listen to the engine carefully. If it sags gradually, it is too rich. You should turn the air-bleed screw OUT 1/8 of a turn, advance the throttle gradually to full for a few seconds, reduce back to idle and listen again. Repeat, until it runs at a stable idle speed.

If, on the other hand, the engine gradually speeds up at idle, it is too lean. Do the exact opposite of the previous paragraph (turning the air-bleed screw IN to enrich).

From this baseline, check transition from idle to full power.
After running the engine at full speed for a few seconds, close to idle and allow it to idle for 30 seconds. Now open the throttle rapidly.

If it immediately accelerates, you are done.

If it sputters fuel before eventually speeding up, or dying, it is too rich, open the air-bleed screw a little and try again.
If it hesitates (coughs...) before eventually speeding up, or dying, it is too lean, close the air-bleed screw a little and try again..