Make sure the spark plug lead has a good connection to the spark plug lead. You might even want to polish the connector with some fine sandpaper. Every time I have had a glitching problem it turned out to be a poor conection in this area.
A good source for shielded braid is your local Home Depot plumbing dept. Get a flexible hose of the right size, cut off the ends and extract the hose out of the braid. Just make sure its copper not stainless or you will have a hard time soldering to it.