I've been flying an old Goldberg Obsession 120 weighing near 14 lbs powered by a DLE 20 and controlled by a 9Cap for about a year now. Overall I've been very impressed with the performance of this engine. Other than not having unlimited vertical or the ability to hover at will, this little gasser does a good job yanking this tank around. My only gripe has been that darn timing curve issue, which always shows it's ugly face when attempting to grease a landing using throttle mangement to control the attitude of the plane just before touchdown.

I've tried tuning it out, played with the geometry of the linkage, applied expo, modified the throttle curve, etc, etc to no avail, the RPM surge, followed by a slow return to idle is still there.

One thing I have observed tho is this. This surge is not so pronounced on the ground (ie. blip the throttle holding the plane). However, when on final for landing with a nice smooth glidepath established (throttle control at idle), you will hear the engine return to full idle suddenly as the plane airspeed reduces to a certain point. My conclusion is that on the ground, the prop is "loaded", but in the air it's "windmilling" to a certain degree which causes it to hang up on the high side of the curve longer.

The first few landings with this plane were interesting to say the least, but now I understand (thanks to observations of others on RCU) what's going on.