know exactly what causes that the 78 xs11 was the fist bike to use a vacuum advance , like a car , to advavane the engigine timing durin acceleration an give better gas milage at the same time . under the round cover onthe left side of engine r the pick up coils for the ignition if u follow the wires from them to where they exit that round area a metal retainr clamps them to the engine the wires r broken inside the insulation there . give the wires one by oneafirm tug there , when u pull the bad oneit will stretch like its made of silly putty. thats becase the wire is broken inside