1984 atc 70

Hello the other day my dog and I were riding around on atc every thing norm as usual when I pulled back to barn with it still running I climbed off and it studded a couple of times like turning the on and off switch would do and about 30 sec goes by it did it but died . So I check the obvious getting gas getting spark .. well to make a long story short the Damm thing only runs when spark plug boot is pulled away from plug moment I put it back on it dies has the best spark than I have ever seen replaced boot coil wire spark plug.. im stumped dogs bummed
Any ideas be greatly appreciated…
Ricko