Some of the CZ-70's display a bit more Sensitivity on a Sens setting of '6'..... and require a setting of '4'. On these 'extra sensitive' CZ-70's......In remote cases, a Sens setting of '6' can be used....... but normally '4' is as high as you can go. There's only about 2% performance difference between 4 vs. 6 on the CZ-70's. (A large difference between 2 vs. 4). Now........ if your detector is unstable at any setting (assuming you tried different physical locations outside)...... and the problem still exists,,,,,, no matter what coil you use; then the unit has a problem. Sometimes humidity/moisture on the Ckt boards (usually from a sudden temperature change) can cause any electronic device to be unstable.
Tom