Bias circuit for change from CDI to CDM?

[Redbarron%%]

I have been trying to figure out the bias circuit used in the CDM ignition to be able to replace the switchboxes on a "Mercury" Force 90 hp engine. I have been on the Force forum here, but I haven been able to get the information yet.
The idea is to replace the switch boxes and individual coils with the CDM modules to clean up the wiring and perhaps make the setup more servicable. I have the red stator with the two wire output and a 3 cylinder harness. The issue I have is the old force flywheel and trigger is stock and does not have the bias circuit buitl in the trigger like the late models with tthe CDM.
The ignition works great except that as the RPM increases the timing increases due to the lack of the bias circuit to increase the negative voltage at the trigger to off set the increasing voltage from the trigger coils with increasing RPM.
The uncompensated trigger coils are biased in the old switchboxes so that is taken care of there in the CDI system.
There must be a circuit I can build external to the trigger coil and CDMs to compensate as there is one built in the new style CDM trigger.
I could buy a late model flywheel and trigger at a cost pretty much equal to the cost of an overhaul, but I feel that there is a way to do this with some parts and labor if I had an insight to the circuit.
I have found a simplified print showing three diodes one from each coil wire to a capacitor, but what value would it be? I have tried this with a value to .3 MFD with little results. I have seen mention of a 4th coil in the trigger perhaps to generate the negative voltage as the other coils generate a positive.
Why not just a new style trigger coil, well the magnets in the central timing of the flywheel are arranged in a push-pull configuration with basically two stacked rings compared to a single ended single stack of magnets in the new.
Any help would be appreciated.

 

[Texasmark]

Look up the energy required to fire a spark plug....like 0.15 Joules (watt seconds) in my recollection but I forget where the decimal is located. I think it's as posted. Taking energy stored in a capacitor as Wc = ½ CVexp2 would be your stored requirement plus I'd add something for circuit losses....course that's the purpose of the ½ preceding energy stored equations for L and C circuits. It's already in the equation.

C in microfarads, V in volts , exp2 = squared.

In the "pulse modulator" design, the capacitor dumps it's total charge into the load on the first quarter cycle. All that remains is a step-up device to match the turns ratio of the capacitor voltage vs the required load. I know Merc has an open circuit voltage of 40kv advertised but I don't know the actual turns ratio of the HV coil. I'd expect the plug to fire around 18kv on the upswing to 40, so you'd have like a 200v cap voltage vs 18kv load voltage.

Edit. Just looked up some numbers on the Cv in my manual for 3-4 cyl 2 strokers. DVA testing (peak input voltage) per the manual, at the input wires to the CDM (using a breakout adapter...circuit still intact, just monitoring what's going on), at idle is 200-350v Cranking trigger voltage range is 0.2 to 2.0.v Looks like pretty sloppy tolerancing as would be the firing voltage of the spark plugs, depending on their condition, so it looks like you get in the general vicinity and you're home free.....would be my guess.