Mercury 79? 70Hp rev counter problem.

[ThomasB81]

Hi..

Can a bad battery cause wrong reading on the rev counter?

The rev signal comes from the stator that also feeds the voltage regulator "yellow wires".

Or can it be a faulty stator?

Charging voltage looks fine.

Thomas.

 

[ajgraz]

Re: Mercury 79? 70Hp rev counter problem.

Have you tried swapping to the other yellow wire for the tach signal? Maybe just one of the two yellow wires from the stator is screwy.

Does the tachometer have a pole setting? For my 1979 70hp 3 cyl Merc I have the pole setting on my Teleflex tach set to 6.

 

[ThomasB81]

Re: Mercury 79? 70Hp rev counter problem.

Have you tried swapping to the other yellow wire for the tach signal? Maybe just one of the two yellow wires from the stator is screwy.

Does the tachometer have a pole setting? For my 1979 70hp 3 cyl Merc I have the pole setting on my Teleflex tach set to 6.

Yep, I tryed the wire swapping to day, that made no difference

My tacho has a pole setting, but it use to work at current setting.

I?ve just mounted a voltageregulator instead of the original rectifier, and the charging voltage looks fine, but it seems to have affected my tacho.

At idle it shows about 800revs, but at full throttel it goes to zero, well thats how it was yesterday. Started at up again to day to check the yellow wire swapping thing, and then it looked fine at idle, a little more throttel it showed about 200 revs less, even more throttel it got up allright, but was a little jumpy.

It is like it acts differently depending on how much current is flowing to my battery.

 

[ajgraz]

Re: Mercury 79? 70Hp rev counter problem.

If you still have it, first thing I'd do is swap the original rectifier back in and see if the tach acts right again. Rule out a broken tach.

Next, do you have specs/manual/sheet on the regulator? What regulator is it, and how's it hooked up? Maybe that'll give us a clue what's up.

 

[ThomasB81]

Re: Mercury 79? 70Hp rev counter problem.

Hi again.

Okey. Here?s the story. I had some problems with overvoltage on my system and I burnt two rectifiers, so i decided to try out the voltage regulator from this thread:

http://forums.iboats.com/showthread.php?t=252684

The regulator is not original and i don?t have any specs on it, but it should do the job. And by the look of it, it does, except my tachometer.

I pulled it all apart to day and measured, volt, amps and frequency from my stator, the reason my tacho is acting funny is the frequency from the stator.

At idle its about 80Hz between one yellow wire and ground. If i give it just a little more throttle, then the frequency drops and so does my tachometer ofcourse.

The frequency between the two yellow wires, follows the engine revs, but between the one yellow and ground "which i think my tachometer gets its reference from" it?s unstable.

Sorry my english, please ask if I?m not clear enough.

Thomas.

 

[sschefer]

Re: Mercury 79? 70Hp rev counter problem.

Hi again.

Okey. Here?s the story. I had some problems with overvoltage on my system and I burnt two rectifiers, so i decided to try out the voltage regulator from this thread:

http://forums.iboats.com/showthread.php?t=252684

The regulator is not original and i don?t have any specs on it, but it should do the job. And by the look of it, it does, except my tachometer.

I pulled it all apart to day and measured, volt, amps and frequency from my stator, the reason my tacho is acting funny is the frequency from the stator.

At idle its about 80Hz between one yellow wire and ground. If i give it just a little more throttle, then the frequency drops and so does my tachometer ofcourse.

The frequency between the two yellow wires, follows the engine revs, but between the one yellow and ground "which i think my tachometer gets its reference from" it?s unstable.

Sorry my english, please ask if I?m not clear enough.

Thomas.

Thomas, it sounds like you have a cracked, broken or loose magnet in your flywheel. This would cause the variations in frequency.

 

[ThomasB81]

Re: Mercury 79? 70Hp rev counter problem.

Thomas, it sounds like you have a cracked, broken or loose magnet in your flywheel. This would cause the variations in frequency.

Yes, I have thought about it, but the frequency between the two yellow wires look fine, so I don?t think there is anything wrong with my flywheel or stator.

But i think im going to pull it of anyway just to bu sure.

 

[sschefer]

Re: Mercury 79? 70Hp rev counter problem.

Yes, I have thought about it, but the frequency between the two yellow wires look fine, so I don?t think there is anything wrong with my flywheel or stator.

But i think im going to pull it of anyway just to bu sure.

Are you checking the freq with a multi meter or a scope. You'd see the spike on a scope if you isolated it from earth. Don't touch the case when you do that, it'll bite.

Not sure why you're showing 80hz. If you're using an anaolg meter you're needle would be bouncing from 800-4800 hz @ 800 RPM. Setting your tach to the 6 pulse setting either tells it to combine the pulses or read only one pulse and shunt the rest, (depends on the quality of the instrument). If your multi-meter had that ability it should be showing 800hz, (800 RPM)

If that 80hz is a true reading then your stator or flywheel magnets are whacked. If you're really reading 800hz-4800hz at 800 RPM idle speed then your tach is shot.

 

[ThomasB81]

Re: Mercury 79? 70Hp rev counter problem.

Are you checking the freq with a multi meter or a scope. You'd see the spike on a scope if you isolated it from earth. Don't touch the case when you do that, it'll bite.

I don?t have a scope, so I did it with a multimeter. The tachometer follows the frequency in the multimeter allright.

 

[sschefer]

Re: Mercury 79? 70Hp rev counter problem.

I don?t have a scope, so I did it with a multimeter. The tachometer follows the frequency in the multimeter allright.

I just updated my last post... Please review it again it might help.

 

[ajgraz]

Re: Mercury 79? 70Hp rev counter problem.

Yes, I have thought about it, but the frequency between the two yellow wires look fine, so I don?t think there is anything wrong with my flywheel or stator.

But i think im going to pull it of anyway just to bu sure.

If you should determine you need a new flywheel, let me know; I have one off a 1979 70hp Merc 3cyl. Only thing wrong with it is the timing decal is worn away.

 

[ThomasB81]

Re: Mercury 79? 70Hp rev counter problem.

I might have found a solution to my problem, just don?t know if i dare to try it out.

http://www.macgregorsailors.com/forum/viewtopic.php?f=8&t=15506&p=186052#p186052

That sounds alot like the same problem i?m having, and he used the same regulator.

Anyone know if there is any risk of damage by using the "Ignition system pulses" for my tachometer instead of the startor pulses?

 

[sschefer]

Re: Mercury 79? 70Hp rev counter problem.

I might have found a solution to my problem, just don?t know if i dare to try it out.

http://www.macgregorsailors.com/forum/viewtopic.php?f=8&t=15506&p=186052#p186052

That sounds alot like the same problem i?m having, and he used the same regulator.

Anyone know if there is any risk of damage by using the "Ignition system pulses" for my tachometer instead of the startor pulses?

Not sure. Why don't you just buy the right rectifier/regulator for it. They're on eBay all the time and cheap.

 

[ThomasB81]

Re: Mercury 79? 70Hp rev counter problem.

Not sure. Why don't you just buy the right rectifier/regulator for it. They're on eBay all the time and cheap.

Well it might end that way, but I would realy like this to work.

 

[ThomasB81]

Re: Mercury 79? 70Hp rev counter problem.

Are you checking the freq with a multi meter or a scope. You'd see the spike on a scope if you isolated it from earth. Don't touch the case when you do that, it'll bite.

Not sure why you're showing 80hz. If you're using an anaolg meter you're needle would be bouncing from 800-4800 hz @ 800 RPM. Setting your tach to the 6 pulse setting either tells it to combine the pulses or read only one pulse and shunt the rest, (depends on the quality of the instrument). If your multi-meter had that ability it should be showing 800hz, (800 RPM)

If that 80hz is a true reading then your stator or flywheel magnets are whacked. If you're really reading 800hz-4800hz at 800 RPM idle speed then your tach is shot.

Just tried every setting on my tachometer, none of them results in correct reading. 6 pulses is stable allright but it dosen?t match the engine revs.

 

[ajgraz]

Re: Mercury 79? 70Hp rev counter problem.

Anyone know if there is any risk of damage by using the "Ignition system pulses" for my tachometer instead of the startor pulses?

Maybe I'm not thinking hard enough, but exactly where would you be getting your tach signal from; that is, where are you going to tap into "ignition system pulses"?

 

[sschefer]

Re: Mercury 79? 70Hp rev counter problem.

You're already using the ignition coils... They are taped differently so they can be included in the charging circuit. Count the larger wired coils and you'll find there are 10. The tach is reading 6 pulses... That tells you right there that the two ignition coils are in the circuit.

Why 6 if you have 12 coils. It's A/C and swings 360 degrees from negative to positive (requires one magnet and two coils or one coil and two magnets). An Analog tach is relatively simple and only reads the positive pulse.

As a side note, those that are wondering why a failed rectifer/regulator kills the spark now know the answer.

 

[ThomasB81]

Re: Mercury 79? 70Hp rev counter problem.

You're already using the ignition coils... They are taped differently so they can be included in the charging circuit. Count the larger wired coils and you'll find there are 10. The tach is reading 6 pulses... That tells you right there that the two ignition coils are in the circuit.

Why 6 if you have 12 coils. It's A/C and swings 360 degrees from negative to positive (requires one magnet and two coils or one coil and two magnets). An Analog tach is relatively simple and only reads the positive pulse.

As a side note, those that are wondering why a failed rectifer/regulator kills the spark now know the answer.

Does this mean that ignition and charging voltage comes from the same coil, and the wires are just connected to different places on the coil? If thats the case, there should be no risk in using one of the wires going to the ignition instead, for my tachometer signal, the difference is that there is no voltage regulator after my tacho signal if I use one of the ignition wires "the red or the blue one".

Maybe that that would make a difference.

Or.. Would this do the trick, and does it have a wire for the tachometer?
http://www.iboats.com/mall/partfinder/?*******=198921785&gd_grid_id=1286&gd_poid=334793&gd_row=61&**********=497010227

 

[ThomasB81]

Re: Mercury 79? 70Hp rev counter problem.

Does this mean that ignition and charging voltage comes from the same coil, and the wires are just connected to different places on the coil? If thats the case, there should be no risk in using one of the wires going to the ignition instead, for my tachometer signal, the difference is that there is no voltage regulator after my tacho signal if I use one of the ignition wires "the red or the blue one".

Maybe that would make a difference.

Or.. Would this do the trick, and does it have a wire for the tachometer?
http://www.iboats.com/mall/partfinder/?*******=198921785&gd_grid_id=1286&gd_poid=334793&gd_row=61&**********=497010227

My stator is only 9amps, but I dont want a "rectifier only" solution again.

 

[sschefer]

Re: Mercury 79? 70Hp rev counter problem.

When you tap either of the yellows for a tach signal, you're doing so before the voltage is recitifed or regulated. The same would hold true for the red or blue. The only time you regulate the voltage to the tach is if the rectifier/regulator has a gray tach wire. I'm not even sure that it's regulated it my be just a convienence outlet so you don't have to tap into the yellow.

The voltage at the red or blue will be much higher than that at the yellow but will not produce as much current. If your tach can handle 200+ volts then it will be fine on the red or blue but if it's designed for 16-18 volts then stick with the yellows.