My Altimatic works perfectly with the following exception. At higher altidudes with four up and the C of G further aft than normal, it has a tendency to "hunt" up and down slightly. Not a big problem as I seldom fly in that configuration, and it hasn't got worse, but recently I discovered I could replicate the problem at any altitude by slowing down to about 120 kts. It holds perfectly as the speed bleeds the back and auto trims, but then starts to pitch up and down quite markedly - more so than in the previously described situation. Kicking out the altitude hold gets rid of the problem - it doesn't occur in pitch mode.
The unit works perfectly in every other configuration. It holds altitude very accurately during turns and speed variations. Problem seems to relate to angle of attack. "Hunting" in altitude hold mode with two previous autopilots (Alt IIIB and Century IV) has been cured by overhauling the pitch servo, but not this time - no change whatsoever.
Any thoughts?
John Moore