I recently replaced all the ignition system chasing a down track misfire. cap-rotor-wires -coil-distributor- plugs ended up fixing the problem even though they looked ok. Yes i kick myself in the butt for that. Should have replace the plugs to start with but live and learn.

I replaced the carb because the new engine needed more cfm. also replaced the fuel pump when it went bad. I had replaced the regulator too as part of the fuel pump diagnosis.

So it seems the only thing I haven't replaced is the msd box it is a 6al
maybe i will try a different msd box. I cant think of anything else. Any other ideas?