You will have to replace your bad ignition coil on your sportster. They are not servicable. Once they are bad they are bad. Make sure you check your entire ignition system before you go and replace it. I believe there is a pickup to tell it when to spark. And your ecm/cdi box
replace it!!! generally around a 100 bucks. before starting,remove your battery this will eliminate possible arc flash. tag your wires as you remove them so you know where they go. remove the bolts from the mounts and the coil is now free. replace with a new coil and reattach wires
These are generally found on the outside and are connected with a bolt or bolts, if it is bad purchase a new one and replace it by removing the bolts and putting the new one on.
Your best bet is simple to buy a new ignition coil and replace the old one you have. It is always best to buy the best quality coil you can, with a warranty of some kind on it if possible.