[rord]

Howdy! My 1979 mercury 80 HP that recently indicated 5200 rpm WOT @ 39 mph, now indicates 4500 rpm WOT @ 39 mph. It also recently started to quit running at random times. The battery starts the beast fine, I cruise for awhile to my next favorite fishing spot and in the process it may or may not quit. If it does, the battery is now dead. I connect a jump pack to it, start it up and it runs fine until the next time. If I shut the motor down as normal, it restarts with the battery like nothing ever happened except for the low tach indication. I have checked for shorted, chaffed, loose and broken wires and can find none. In concept, it appears the tach signal may be missing a pulse or two? Any assistance the experts can provide would be greatly appreciated. Thank you!

[CharlieB]

The tach is actually just a volt meter with a different face. A failing tach is often a sign that the stator is loosing output, though not always, coupled with battery dying, I would start with fully charging your battery with a small amp trickle charger, then test battery voltage both engine off and engine on, at idle and at 1800 - 2000 to see it the charging system is working 'up to snuff'.

[rord]

Hi CharlieB, thank you for your reply and recommendations. I will perform the tests and provide an update as soon as I get her back on the water.