G'day Johno,
First thing i would do is increase the size of hook to 3/0 to 5/0, both are available in 1/8oz.
Secondly pay very good attention to how straight the jerkbait sits on the jighead. It must be straight looking from above and the side. Mostly my baits will slowly spiral down and probably do a full turn every 4 or 5 feet they drop. I have had a few that didnt and there was not any difference in the strike rates. If it spirals quickly it definitely will not be as effective.
Thirdly what weight line are you using?? It could be stiff and generating some tortion with the twist that generates in your line each cast. Some spinning reels overcome this with a anti-twist bail roller. It might pay to tie a small loop knot and see if that reduces your spiraling down.
Jack.