Mercury 79? 70Hp rev counter problem.

[Faztbullet]

Re: Mercury 79? 70Hp rev counter problem.

A outboard tach operates by reading the unregulated AC output of the charging system(stator) and the electrical pulses per revolution are equal to 1/2 of the alternator poles.

You're already using the ignition coils... They are taped differently so they can be included in the charging circuit.

High speed and low speed coils are not tapped into charging circuit!!!

I would have to look and see but the older forces had a 20 pole stator and the newer tachs do not support a 20 pole setting, the rectifier shouldnt make a difference unless its feeding DC to tach instead of AC..

 

[sschefer]

Re: Mercury 79? 70Hp rev counter problem.

A outboard tach operates by reading the unregulated AC output of the charging system(stator) and the electrical pulses per revolution are equal to 1/2 of the alternator poles.



High speed and low speed coils are not tapped into charging circuit!!!

I would have to look and see but the older forces had a 20 pole stator and the newer tachs do not support a 20 pole setting, the rectifier shouldnt make a difference unless its feeding DC to tach instead of AC..

Yep, they are. Short out a rectifier and watch the spark go away... I have an old 9 amp all torn apart cuz I wanted to find out. Suprised me too.

 

[Faztbullet]

Re: Mercury 79? 70Hp rev counter problem.

Yep, they are. Short out a rectifier and watch the spark go away

Here is factory ignition circuit for a V-6 same a 3 cylinder, where does it show the charging circuit tied in??? Its not, as if it was you would be able to read thru the winding from either the blue or red to a yellow charge wire and only way to block it from feeding back on itself would be a diode in circuit which it does not have. The reason spark dies on a shorted rectifier/stator is it shorts stator to ground thus making it overheat( your making a heating element). You need to test the system with a meter with a DVA adapter as 99% of the meters will only pick up the average or RMS voltage not the peak voltage reading. A simple test for this engine is to start it and bring it to 1200-1500rpm and DVA test each yellow wire to rectifier. The voltage readings should be within 1-1/2 volts of each other, i.e, if one wire reads 20 volt the other must read 18.5 to 21.5 volts. If one wire reads low,stop engine and swap the wires on rectifier and restart and test, if problem followed wire stator is bad ,if problem didnt move rectifier is bad and if both check out ok the wiring to tach or tach is bad.

 

[sschefer]

Re: Mercury 79? 70Hp rev counter problem.

Here is factory ignition circuit for a V-6 same a 3 cylinder, where does it show the charging circuit tied in??? Its not, as if it was you would be able to read thru the winding from either the blue or red to a yellow charge wire and only way to block it from feeding back on itself would be a diode in circuit which it does not have. The reason spark dies on a shorted rectifier/stator is it shorts stator to ground thus making it overheat( your making a heating element). You need to test the system with a meter with a DVA adapter as 99% of the meters will only pick up the average or RMS voltage not the peak voltage reading. A simple test for this engine is to start it and bring it to 1200-1500rpm and DVA test each yellow wire to rectifier. The voltage readings should be within 1-1/2 volts of each other, i.e, if one wire reads 20 volt the other must read 18.5 to 21.5 volts. If one wire reads low,stop engine and swap the wires on rectifier and restart and test, if problem followed wire stator is bad ,if problem didnt move rectifier is bad and if both check out ok the wiring to tach or tach is bad.

Don't always trust what you see in the diagrams. CDI and Merc tells you to disconnect the rectifer/regulator in a no spark condition. If they weren't tied in then that test would be frivolus.

 

[Faztbullet]

Re: Mercury 79? 70Hp rev counter problem.

Thats the FACTORY schematic, and its the same one that CDI, AMTEC and MERC uses in the service schools, so I highly doubt its wrong... The only thing they have in common is they are on the same stator frame.

 

[sschefer]

Re: Mercury 79? 70Hp rev counter problem.

Whatever.

 

[ThomasB81]

Re: Mercury 79? 70Hp rev counter problem.

Hi.

Just to end this story.

I bought a CDI 194-5279 instead and now everything works incl. tachometer.

Thomas.