Trouble with my tachometer.

[Tompasio]

This is rather funny, Sometimes when i drive the tach shows 4000 rpm,and suddenly drops to 2500 rpm and then suddenly raises to 4000 rpm again.But the engine are not drop a single rpm.What can cause this?
GSX 750 es 1983 16valve.

[Dave8338]

Sounds like the tach is getting a little sticky up in the head unit. Try pulling it apart and cleaning it up with some spray carb clean, blow dry the thing and some spray silicone lube should get you back in business...

[duaneage]

Pull the wire for the tachometer cable out, it could be frayed and on it's last leg.

[rudy]

The tach on the 85 750EF I just picked up does the same. It only goes to 4000 and stops. I haven't had time to pull it all apart yet, but I figure there's got to be either a problem with the cable, or the unit is dirty inside. Not a hard fix, do as Dave says.

[tkent02]

That's an electronic tachometer, they seem to have these problems, at least on the 750s.
Mine always got stuck at around 5,000, then worked correctly above about 7,000.
Someone with some electronic troubleshooting abilities needs to tear one apart and find a fix.

[Tompasio]

Yeah, Its an electronic tacho.

[Dave8338]

Either way mechanical or electronic, there is too much resistance. Check the wires, their connections, and the internals of the tach. Could also be an issue with the printed circuit board and or its' parts.

[Tompasio]

Ok thanks, will check the wires and their connections,

[Tompasio]

Does the tach measures revs from the coils or from the signal-pickup ?