28-05-19, 05:34 PM
I see you’d checked the plugs were all sparking, but they can behave differently when out.
Have the plug caps ever been changed? If they’re the originals (black right angle) then they’re renowned for causing misfires, if they're straight red ones they've been changed for NGK SD05F type which are more dependable.
It's also worth trimming the lead where it screws into the plug cap, the wire core can corrode… lopping 8mm or so off the end gives the screw something conductive again.