Sorry that I could not be any more help !
I have disused this problem with some engine builders that I no and one has said that some years ago he blow 2 coils it turned out to be a problem with the fly wheel or the gray coil he is not sure which one but is going to it up and get back to me he suggests that you do not fit another one until you have checked out flywheel and gray coil ? as soon as he gets back to me I will post it !
good luck this is a very expensive problem if you live in the UK as the red coil is £ 55-00 here thats about $ 80-00 US