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Tachometer output on 50 Hp Mercury four stroke

  
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Rod McInnis

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Since: Oct 20, 2003
Posts: 304



(Msg. 1) Posted: Wed Jun 23, 2004 1:16 pm
Post subject: Tachometer output on 50 Hp Mercury four stroke
Archived from groups: rec>boats (more info?)
Model year 2000, Mercury 50 Hp, fourstroke, "Big Foot". Carbureted engine.

My troubles with these engine never seems to cease.

Finally got the motors running half way decent, but now the tachometer for
one engine has stopped working. I swapped wires at the helm station between
port and starboard engines and the problem followed the engine, the tach
works fine.

I have an after market manual on the engine that provides a wiring diagram
but I can't figure out what the tach output is. There isn't a whole lot to
the electronics (except big and probably expensive modules). The engine
runs fine, but I suspect that the charging circuit is a little weak. With
the engine rev'ed up fairly high I was getting 13.0 volts at the battery
(pretty close to fully charged, it was at 12.7 before I started the engine)
so I am getting at least some charge. I am not too concerned about the rate
of charge but I suspect that the tachometer output might be related to the
charging circuit.

Can anyone give me a guess as to what I need to change to make this thing
work? I really need the tach. I can't really hear the engines from the
helm station (houseboat) and without the tach I can't tell if the engines
are anywhere close to running the same.

Rod

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Greg1

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Since: Jan 04, 2004
Posts: 307



(Msg. 2) Posted: Wed Jun 23, 2004 9:08 pm
Post subject: Re: Tachometer output on 50 Hp Mercury four stroke [Login to view extended thread Info.]
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The tach does use the charging system, picking up the unregulated AC input to
the rectifier.I would look for a loose connection before I started thinking
"stator".

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IBNFSHN

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Since: May 30, 2004
Posts: 35



(Msg. 3) Posted: Wed Jun 23, 2004 9:38 pm
Post subject: Re: Tachometer output on 50 Hp Mercury four stroke [Login to view extended thread Info.]
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A shorted rectifier will keep your tach from working too.

--
Bill
Chesapeake, Va


"Greg" wrote in message

 > The tach does use the charging system, picking up the unregulated AC input
to
 > the rectifier.I would look for a loose connection before I started
thinking
 > "stator".
 >> Stay informed about: Tachometer output on 50 Hp Mercury four stroke 
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Rod McInnis

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Since: Oct 20, 2003
Posts: 304



(Msg. 4) Posted: Thu Jun 24, 2004 3:29 pm
Post subject: Re: Tachometer output on 50 Hp Mercury four stroke [Login to view extended thread Info.]
Archived from groups: per prev. post (more info?)
"Greg" wrote in message

 > The tach does use the charging system, picking up the unregulated AC input
to
 > the rectifier.I would look for a loose connection before I started
thinking
 > "stator".

I would really like to think that it was a loose connection, but I have
examined the motor and couldn't find one.

A bit of history: I bought this houseboat a year ago. The motors ran very
poorly at low RPMs, and after 6 months of diddling with them I had the boat
hauled out, took the motors off and brought them to a Mercury factory
service center. The Tachs on both motors worked when I took the motors off.

When I put the motors back on I think that the tach worked. By the time the
boat was put back in the water, however, the port engine no longer had a
working tach. I figured that it was just a loose wire and I would fix it
once I got back to my slip.

When I got the boat back I popped the covers off both engines and inspected.
They are both hooked up the same, but the port engine has no tach reading.

I will be anchoring out this weekend and will use the opportunity to check
the charging system out. I suspect that the port motor is very weak in
charging but it was hard to tell because when I tested it the battery was
fully charged. After being anchored out for a day the battery should be
sufficiently discharged that I can better see the charge/voltage levels.

I could live without the charging circuit. I can't live without the tach.

Man, I am beginning to hate outboards.....


Rod
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Peter W. Meek

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Since: May 18, 2004
Posts: 5



(Msg. 5) Posted: Fri Jun 25, 2004 11:01 am
Post subject: Re: Tachometer output on 50 Hp Mercury four stroke [Login to view extended thread Info.]
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On Thu, 24 Jun 2004 12:29:40 -0700, "Rod McInnis"
wrote:

 >I will be anchoring out this weekend and will use the opportunity to check
 >the charging system out. I suspect that the port motor is very weak in
 >charging but it was hard to tell because when I tested it the battery was
 >fully charged. After being anchored out for a day the battery should be
 >sufficiently discharged that I can better see the charge/voltage levels.

A common outboard tach pulse source is from the output
of the alternator (pre-rectifier). If you can come up
with a portable oscilloscope, you might try comparing
various points on the port and stbd motors to see
what's different. I always liked diagnostics on stereo
systems with one bad channel -- I had a good version
to compare with the bad. Even a decent volt meter should
give you some clues as to where to start.
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