Running On Two

Out on the bike toady for a ride all went well had to go to reserve then filled up, no probs stopped for tea then set off back been running for 20miles or so when backfire from one side and bikes running on two cyls and cutting in and out of three, first thought bit of muck in fuel but then wondered about coils, still on old ones, what would be the symptoms of a coil breaking down?

 

How do i get hold of Paul Messenger to order a set of stick coils ?