Advice on fish finder transducer installation

[mikerino]

Hi all, I installed a Humminbird chirp 5 in my 2006 sportster and planned to install the transducer through the hull. I followed the advice about putting it in a ziplock full of water and trying different locations, when I found one I glued it down with slow cure epoxy but it didn't work. It show hundreds of feet of depth when it is should be about 10 feet. Kind of giving up on through the hull. Any advice on installing it outside? I have seen threads about putting it by the speedo sensor. Is it OK to use the self tapping screw that comes with the mounting kit? All advice appreciated.