Engine missing weak spark
 

Hey all! My 79 930 has a low rpm miss and hesitation. I thought fuel related for the longest but I have investigated from both fps, filter and a/f ratios. It appears Im getting fuel, It runs strong when I get on it but has a miss a times at low rpms and cruising. Sometimes its better than others. I have changed the coil, plugs and wires replaced, cap and rotor was inspected, not by me though. I need some direction on what else can cause a weak or irradic spark. Distributer? Anyone else experience something simular? Thanks, Mark

Maybe the capacitive discharge box, but its been my experience that these just die or intermitantly cut, not get weak.
How about the distributer shaft? does it have any play? That could be a problem.
Maybe a MSD unit is in order, they are pretty simple to install.