First, when you adjust the low end, the engine should have been running for about 2 - 3 minutes so it is completely warmed up. Your trim for the throttle should be adjusted so that at 1/2 - 2/3 of the way is where you start the engine and about 1/4 - 1/3 of the way open is where it should idle with the throttle stick fully closed. After you have adjusted the idle AND trim, start the engine, make sure everything is OK (high speed needle), taxi out to the flight line, REDUCE THE TRIM to the idle position, THEN take off. Set this way, you can kill the engine by fully closing the trim. Once you have set the low end, you should not have to touch it again.

Another thing to keep in mind/check is the brand of propellor.

An APC prop is more efficient than a Master Airscrew prop. This is due to the blade shape.

If you are presently using an APC prop (the grey props), try a Master Airscrew (the black props) of the same size. What you will notice is the following: The Master Airscrew will create a little more noise, the plane will slow down faster and MAY also idle lower due to the wider blade (more resistance) and you will loose a little on the top end which is rarely noticeable. If you are presently using a Master Airscrew, drop down one size in the pitch and/or go up one inch in diameter.

On the reverse of this - using an APC instead of a Master Airscrew. I have seen a NOTICEABLE difference in power/performance and a lower noise level.

Most of my planes use an APC prop, however, on two of them I use a Master Airscrew because the APC has too much thrust. On my Rascal 40 (46 FX) I switched to a Master Airscrew because the ONLY WAY I could land with the APC was to kill the engine. On my Rearwin Speedster I switched to a Master Airscrew so it would slow down more for landing (I really dislike landing "hot").

Hope this helps.