With any gyro setup you should always make sure that your mechanical setup is spot on to start with.
There should be no slop or binding of any of the linkages, and everything should feel tight and direct.
I used the HK401B which is a knock off of the Futaba 401 but for considerably less cost. Its not as good as a real 401 but its a lot better than its price would suggest!
Couple this with a decent fast digital servo and you have a great system for the money.
You must pull the gyro apart though and do the 2 Minute Mod to be sure it will work to its best.
Once you have your linkages sorted out, setup your servo arm and ball joint. Ball should be approx. 7-8mm out from the centre of the horn for best response.
Place the tail slider so that its mid way in its travel, servo arm should be pointing straight up at 90 degrees to the direction of travel. You might have to move the servo on the tail boom to get this correct.
Now make sure you have no trims or adjustments etc on your rudder channel and set the limits on your HK401B gyro. Limits should be around the 100 mark on the adjustment pot, if they are more move the ball on the servo arm to the next hole out.
You can lose gyro resolution if the limits are set too high or low!
Heading hold mode automatically sets its neutral limits when you first turn the tranmitter on, based on the neutral position of the servo from the last flight etc.
The HK401B operates in two modes, with gain at 0-50% you are in rate mode, at 51-100% you will be in heading hold mode.
I assign a switch to these so I can easily switch between them.
If you trim the rudder and you want to reset the neutral you have to land, switch between rate mode and heading hold mode 3 times which relearns the new neutral point, and away you go.
Now like I said this HK401B is tremendous value for money, it holds way better than the Telebee I had on my old TRex 450.
For further info on radio setup please refer to my Turnigy Setup.