Strange Behavior When Tackometer Was Disconnected...

Hello,

After sitting for six years or so I'm putting my '87 back on the road. I was in the midst of doing a bunch of work to it when I got wrapped up in other things. To make a long story short, I have a gauge cluster from an '88 I picked up from a U.K. vendor and noticed that the tachometer does not work. I checked for a tack signal on the wire that goes to it and it appears that I do as much as I can tell from my meter which appears to not be working very well. To see if the results I was getting might change with the wire to the tach disconnected, I unscrewed it at the front of the cluster. However as soon as I did that, the speed of the engine picked up by a hundred or so RPM and smoke started coming from the vicinity of the rectifier. I could see if there was an internal short within the tach suppressing the ignition system and effecting the engine speed, but how would that effect the charging system??? Any thoughts?

Thank you,

Rick

P.S. The title should read 'Strange Behavior When TACHOMETER Was Disconnected...not 'tackometer':/

 

That is strange. The VFR ignition went "digital" in 87. All my experience and bikes are 86 "analog" bikes.

Sounds like the system is depending on a signal from the tach to function properly.
Why something started smoking?... yikes.

 

The tachometer on your '87 is a standard, old-school type of tachometer. It is a "Galvanometer" instrument, which means it has two wires that actually operate/actuate it (you have to identify and ignore the other power and ground wires that go to the instrument lighting in the gauge):

one of the wires that actuate the tachometer is a 12volt power supply ("on" any time you have the bike key-switched to "on" or when bike is running), the other wire is connected to one of the coil control wires from the bike's Ignition Control Box (this wire will provide a path-to-ground for each 360 degree of engine rotation).

So the question is this: when you say that you disconnected "the wire to the tach" which wire did you actually disconnect? If you disconnected the 12volt supply to the tach and then accidentally allowed that disconnected wire to touch metal somewhere on the bike you sure will get smoke from somewhere (like the Regulator/Rectifier).

 

Thank you for your input. The wire I disconnected was the 'tach' signal wire, not the +12V or ground connection. I'm thinking I could swap the tachometer from my '87 cluster, or at least the electronics. I'm not sure at the moment, but I believe it would be a direct swap. The clusters overall look very much the same, but the later model has some extra stuff on it like a clock, a fuel lever gauge, and a kick stand warning lamp. I'll be able to look at it more closely on Sunday evening..