Set the timing, correctly first. Verify by tracing from the plug to the cap all the wires are in the correct position.
-11 deg will cause a lean running condition, and will cause a miss fire/back fire while driving.
The first one I worked on , some tech had swapped distributors, and did not time either one. The engine would misfire , and we worked for two weeks trying to fix it. had GM send an engineer out, and the only thing we saw abnormal was the cam offset was at -11 deg. no one new how to set it, or what it was to be set to. once we found out from engineering how to set it and the spec. we set it to 0 deg and the miss went away.
three weeks later the other truck came in with the same complaints. We knew how to fix it by then.
Unless you have the gaskets on wrong or are not sealing, and the wires are on correctly , new cap and rotor, and this was not there before. Then set the timing back to where it was before you started and see if the miss goes away.
Timing must be at 0 deg, the computer uses this as base timing, and will advance from there. It doesn't know the exact timing, only what the timing is from the base setting.