Pull the wire from tach and engine and check with an Ohm meter for partial
shorts. Should be infinite resistance.
Bill

"Ed Barchetta" wrote in message
om...
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?

Thanks,
Ed