Sounds like you're using the stock 3 in 1 together with the 240. Have you tried turning down the middle pot all the way to CCW and then adding just a little bit? My best results were to set up the stock system to fly holding a heading as accurately as possible without tail wag, then adding the HH gyro without changing anything on the 3 in 1. The way the settings ended up were the middle pot was turned to about 6 o'clock and the bottom was pointing to about 2 o'clock.