1997 115 Mercury Tach Problems...

[HammytheFisherman]

Purchased a used boat about a month ago. She has been running fairly well, however, I just began noticing the tach reading ridiculous numbers. Motor (as in title) is a 1997 Mercury 115HP. At times, the tach will read around 3k while in idle. Fifteen minutes later, she will read under 1k for idle (more of the norm). There are times that the tach reads I am running WOT when the engine sounds like she is barely working. Other times, she will read accurate when at WOT and the boat is running like a champion up on plane.

Is this something as simple as checking all connections and cleaning them if needed? I plan to look at the connections tomorrow, but my trailer is being inspected right now so I lack the ability to maneuver outside of the boat. I've read threads about adjusting the settings on the rear of the tach. I'll have to look at the back of mine to see what it looks like back there. Is a new tach ever recommended? If so, how complicated is the install? I've been dealing with the tach issues, but its starting to be annoying when it reads extremely high. Any help or suggestions?

[ricksrster]

Make sure the tach switch on the back of the tach is set to 12 pole/6 pulse. usually indicated by 6P and not in between two positions.