Hi it's defiantly an electrical problem.
It's strange, one minute it'll be running fine then the bottom cylinder will just cut out and will stop working for about 15 seconds sometimes longer then will come back in and run fine for a bit and the same will happen again. When its running and it cuts out if I pull the spark plug cap off the spark plug until I hear it sparking to the plug it'll cut back in again and run fine with the cap loose but if I put the cap back on properly it'll run for a bit but then cut out again !! I just cant understand that when the cylinder isn't running how does it start running again fine just by me pulling the cap of the plug ?? It does this every time so isnt coincidence.
I've put brand new plugs in it and I've changed the cap so it's either the ht lead or the coil but its always getting a spark ??

You guys seem to know your stuff so do you have any ideas ?? Thanks again any help is appreciated.