1978 Mercury Tower of Power 900 lost power after CDI regulator/rectifier installation

[Rstacy]

I have a 78 Mercury 900 that was running great but putting out way too much voltage for any of today's add on electronics. It had the original rectifier only configuration.
​After some research I purchased the more expensive CDI regulator/rectifier over the cheaper solutions.
​The CDI unit did exactly what it was supposed to do. Charge voltage was good.
Unfortunately the engine doesn't like it. I lost about 900 rpms off the top end and at WOT the engine is surging.
​I installed the original rectifier and all was good again as far as engine performance goes.
​Is it possible that the ignition module needs that higher voltage to fire the plugs at WOT?
​If so, any thoughts on how to control the charge voltage without hurting engine performance?

 

[jimmbo]

Install a voltage regulator on wire(s) feeding the electronics that are so sensitive

 

[Chris1956]

Gee, a 1978 90HP inline six should have battery powered CDI Ignition. The charging system is separate, and not connected to the ignition system, Maybe the battery voltage at the switchbox is low, due to some dirty wires?

 

[Rstacy]

Install a voltage regulator on wire(s) feeding the electronics that are so sensitive

Thanks guys. This is one of the ideas that has been bouncing around in my head.
I guess I wanted the folks here to confirm that the ignition system required that much voltage to operate.

Gee, a 1978 90HP inline six should have battery powered CDI Ignition. The charging system is separate, and not connected to the ignition system, Maybe the battery voltage at the switchbox is low, due to some dirty wires?

The wiring harness was replaced last year. I know that doesn't mean much and maybe I have overlooked the obvious.

I need to go find a wiring diagram for this engine.

 

[Rstacy]

The switch box has 2 voltage inputs. One is the switched 12V from the key. I assume that this line turns the box on.
The second line is direct from the rectifier and is the full unregulated voltage.
My thought is to break the line and install a regulator after this connection. Please see attached picture with my notes. Let me know if you agree.

Where can I find a regulator that will pass the voltage if it is 14.4 or less and regulate it if the voltage is higher?

 

[Chris1956]

The red terminal on the switchbox should have the battery connected to it, and it should have +12VDC on it at all times. Look on the max rules site for a wiring diaghram.

The + post of the rectifier should also connect to the battery. The battery acts as a load to regulate the voltage. If the connection to the battery is bad, maybe that allows the charging voltage to rise.

A zener diode of 14V, will shunt all current to ground, if the voltage is above 14VDC. A crude kind of VR, if you can find one.

 

[Rstacy]

A zener diode of 14V, will shunt all current to ground, if the voltage is above 14VDC. A crude kind of VR, if you can find one.

Thanks Chris. The zener diode is an excellent idea and it was pretty easy to find one. I will check the battery connection first.
Raay