Tach jumping around!!!!!!!!!

[MPII]

1992 Rinker 4.3 Merc. LX Alpha I, Gen. II. Two batteries with a Perko switch.

Took the boat out of storage and after rebuilding the Carb, I was adjusting the air micture screws. Upon paying close attention to the tach, I noticed it was jumping around. I tapped on it and it moved around.

Yes, I did search the threads and found a couple emails but nothing adequate to answer my questions so I decided to post the questions.

I have to admit, I have no idea how tachs work, except to say, don't they normally hook up to the #1 cylinder? I checked the wires on the back of the guage and none of the wires were loose.

Any help would be appreciated.

 

[etracer68]

Re: Tach jumping around!!!!!!!!!

I would say on an inboard motor, the tach should be getting the signal from the coil. Some newer motors may have crank, or cam pick-ups.

 

[NEOK]

Re: Tach jumping around!!!!!!!!!

I don't know if this would apply to your inboard, but I had my tach jump on my Mariner 175 outboard last fall. It turned out to be a tack wire that was up against the block and had partially melted the insulation.

 

[Silvertip]

Re: Tach jumping around!!!!!!!!!

The tach on a I/O indeed is fed by the coil -- not a spark plug wire or any given cylinder. if you tap on it and it jumps, then there is either an internal or external connection issue.

 

[pvancorenland]

Re: Tach jumping around!!!!!!!!!

I had the same thing, so I took the tach apart and looked at the insides. I gave is some test signals and it seemed to work. I put everything back together and it's working just fine.
In the end, I think that it's the disconnecting/reconnecting of the wires that did it, not opening up the unit.