1983 Suzuki GS750ES Erratic Tach Operation

[charlie27]

hi, I am having erratic tach operation and not sure what to look at. This is an electronic tach. Jumps all over the place when revving. Idle is fine.Any suggestions welcomed.

thanks

[kingofvenus]

Very common with them. There might be a fix for them, i ditched mine for an aftermarket Koso unit.

[glib]

My GS1100ES was like that prior to rearranging the wiring with the single point ground (according to posplayr's instructions) and replacing the stator with a new Electrosport (mine was fried) and new Compufire R/R. It's not perfect but significantly better now.

[charlie27]

yes, I am suspecting a bad ground. I will recheck all the grounds and see what the resistance is on the ground. thanks

[bobgroger]

Another point to check is if you have solid core plug wires. They will generate enough interference to mess up electronic devices.

[posplayr]

If everything is stock, I would guess that there are some electrolytic capacitors that have gone bad in the tach unit itself. This probably makes the unit more susceptible to noise. The R/R's do generate a lot of noise. I did not think that a SPG would improve the noise, but then again it is no suprise either.

There are two approaches I can think of if you are trying to retain a stock setup:

1.) check the PCB in the Tach to see if there are any obvious failures, that can be swapped out.
2.) Improve the signal conditioning on the input to the Tach using a series resistor (10K) with a 5V zener to ground.

[posplayr]

Here is some discussion of transients on a tach signal, and how to limit positive and negative going spikes.

http://www.thegsresources.com/_forum/showthread.php?240184-Trail-Tech-Vapor-Tach-Problems&p=2331818#post2331818

[charlie27]

on the 85 GS750es the tach signal comes from the ignitor and the same signal used to control one of the dual coils.

[posplayr]

on the 85 GS750es the tach signal comes from the ignitor and the same signal used to control one of the dual coils.

Most of them do. I think some aftermarket ignitions will generate a "clean" 5V tach signal to avoid these issues. The negative side of a coil see transients up to +50v and probably -10v at least