Hey all. My brother has a 69 cougar with a 347 stroker. Car is running msd digital 6 box, and fast ez efi. His having a problem with backfiring out the exhaust while at a cruise. He called fast and they are kind of stumped. They sent out a new computer but that did nothing. Timing is locked out at 28 degrees. Can't find any vacuum or exhaust leaks. Any ideas?