So I've been chasing ignition problems lately (see my post re 123IgnitionUSA dizzy and melted cap center button), so I've been going over my total spark system looking for problems. I (re)-discovered one issue with the plugs. Years ago I had a persistent misfire and finally started swapping out plugs one at a time until I found the culprit. You may not be aware that the tip of these plugs is threaded on. That tip screws right off. There was one plug with a VERY loose cap. Threaded it back on