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On 17 Feb 2004 02:40:53 -0800, (Ed
Barchetta) wrote:

This problem popped up after a trip to the mechanic and he suggested
that it might take some time $$ to diagnose. Hopefully someone has
seen this before. I've got a 1982 Mercruiser 140 (181) that developed
a rough disposition after a few minutes on the water recently. It
started 'coughing' at planing speed and then idled bad to the point of
stalling, even back on the trailer. While the engine would be
sputtering, the tach would show the opposite of what was going on, ie:
when the engine would nearly stall the tach would jump up erratically
and alternately nearly bottom out when the rpm's rose. I found that if
I disconnected the tach connection on the coil, the engine idled and
cruised normally. The wire goes from the coil, through the
throttle/shifter and then to the tach. To eliminate (or verify) that
the tach itself might be the problem, I disconnected it at it's end
and reconnected the coil end. The rough engine returned immediately.
Without tearing out the wiring, I'm guessing a short or disconnection
in the throttle area but don't really know what to expect once I'm in
there. Has anybody any suggestions or experience with such a problem?

Here's a couple of suggestions, although these might not be the
answer.

Check the wire along it's route for abrasion, cracked insulation, etc.
You might also want your mechanic to test the coil. Pull the tach and
try it on another engine. I would suspect either the tach itself or a
short somewhere along the wiring route.

I'm not familiar with the throttle system you use, but I have worked
on a similar age Merc throttle control and I believe the tach wire,
along with temp sensor, oil pressure etc., went to a connector block
and then to the instruments. Pull the connector apart and check for
corrosion, shorts, etc.

Common sense when looking and if necessary, making a drawing of what
you take apart if you take something apart, is a good idea.

Good luck.

Later,

Tom
S. Woodstock, CT
----------

"Fisherman are born honest, but they get
over it." - Ed Zern

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