Something I have noticed with the few mods I have made is that making any changes to how 'easy' or how 'hard' it is to draw the air through an atomizer can make quite huge differences to how well the atomizer vapes and even how well the cart exchanges juice with the atomizer. This isn't a problem if you have used the battery fitting from an old e-cig for the mod because it works exactly the same as it did before (unless you have made voltage changes) but if you do use any other methods of making the battery connection to the atomizer and you find that if it doesn't seem to be working very well, it might only be a problem with the air flow.