ok guys, I just swapped in an HEI unit out of an 81 model. put on new plugwires, and I lined up the rotor with the old one when I replaced it. well now I'm not getting any fire, it rolls over and I've turned it a hundred times it seems like, but all I ever get is backfire through the carb or gas blowing out of the carb. I hooked the yellow wire up to the connector on the HEI unit. Am I missing something. HELP.