SPARK PLUG CAP JUMPING OFF

[torino68]

Hi Cobba, thanks for the thoughts about the exhaust but as you said you see from the photo the exhaust runs beside the barrels, and about 3 cms out from the side so I don't think it would be affecting the head too much. I also wondered if the custom exhaust might be affecting something where it actually exits the head but there is nothing different there to original. Also I had this new exhaust on for about 4 months before the problem started so maybe its not that. I pulled the plugs out yesterday and they seem to be fine, so I swapped them over to opposite sides, took it for a spin and it ran fine. Maybe it will be okay now with the small section cut out of the upper grommet. Time and distance will tell I guess. Thanks to all for suggestions.