You have enough ignition that the plugs should not have any color on the porcelain. If there is color there, it’s rich at idle, and I’d probably say pig rich.
Yes, pig rich at idle gives the opportunity for fuel to enter the exhaust system during the open valves at overlap during idle from the big cam that is in there.
Now all you need is a misfire spark to set it all off and Bang, there's your Backfire again.
