Take the spark plug wire off the side that it's happening on and look at the coil side connection. The type of connector Triumph uses has a tendency to keep spreading and become loose. Take a pair of pliers and squeeze it closed a bit. Pull the boot back about an inch. Pinch the wire just behind the connector with your fingers and plug into the coil. You should feel it snap on tight. Then push the boot forward over the coil nipple. If you still have problems buy a new set of wires from Brent.
