tryin to break in new engine, ruff idle

I kinda had a similar prob years ago...except a loud pop every so often....although I didnt have the electronic conversion I had put in an accell supercoil and distributor....well I didnt put a ballast resistor between coil and distributor...it was getting to much power and causing it to cross fire....dont know if it helps but just a guess...but it does sound like a timing issue