g,day Newman,what make & model are we talking?it could be a number of things,low speed windings often fail, you can test them with a multimeter if you know the specs,you can send all your electics to a rewinder such as small coil rewinds in geelong & they will test for you to diagnose the problem,in the meantime disconnect the killswitch & check & clean all conectors & earth wires,can you borrow coil & cdi off someone with the same bike? cheers Smed