Suggest you check blade that secures opening point isn't proud enough to touch the copper strip inside the cover, and that the swipe-contact is square onto the head of the cb centre screw.
A K1F type plain clip-on cover will go straight on - no kill facility though - or you can get more complicated and change end housing for a sort that takes an alloy dome, or a screw-on large cover, but that probably isn't a great plan due to work involved and problems of mix 'n match.
Ought to be poss to make the one you've got work OK with any luck.
