tachy issues

[jtcrespo]

83' GS750ES, close to 7,000 miles

Bike has no other issues that I know of yet, but the tach has suddenly decided it doesn't want to read past 4,000rpm. On acceleration it will start to wind it's way back down as rpm increases. Almost as if there is a polarity issue above 4,000. All electrics seem fine and there is nothing visibly blocking the needle on the guage face. Engine is turning well above 4,000 and the problem occurs in neutral as well as in gear.

What is going on and how can I fix it?

[Anonymous]

Is it an electronic tach? Mine has something of the same issue, but is electronic. Do a search, and you will find the issue with electric tachs was due to some failing diodes that can be replaced....

[jtcrespo]

Thanks for your quick reponse!

Found the posts, will try Karl Zellner's fix of changing the two capacitors on the circuit board. I'm off work for the next couple of weeks, so I'll add this to my "bike projects" time.

[argonsagas]

If it is a mechanical tach, remove the cable at the engine side and check the end fitting. There is a small fitting with a forked end, and is held there by friction. Sometimes, it comes loose, and allows the cable to move inside it.

If this is the case, you may be able to crimp it and restore full use of the tach immediately.

Use a pair of pliers with a good curved bite to do this. If the fitting is very loose, you could clean it and put a dab of epoxy on it before crimping, or take another extra step and file/grind away a bit from the end of the cable to make a flat spot, which will allow better purchase.

Also note, it would be best to remove the cable from the sheath and hold it in a vise when doing this, so you avoid all possibility of accidentally bending the forks. The fitting is made of very soft white metal, and if you bend it at all, it may break when being straightened. (Not that I have done that in the last month or so but mine now has a custom-made brass end-fitting.)

[jtcrespo]

Thanks! If it's mechanical, I'll keep that in mind. I won't have time to even look and see until next week, but wanted to post and get started on ideas.

I like to look at something and have an idea of what's wrong, before I take it apart, not during or after. That gets me in too much trouble.

[kz]

Thanks for your quick reponse!

Found the posts, will try Karl Zellner's fix of changing the two capacitors on the circuit board. I'm off work for the next couple of weeks, so I'll add this to my "bike projects" time.

Hope the capacitor fix, will do the trick for you as well, my tach worked until I changed the complete dash one year ago...

It probably still works if I remount it.

[jtcrespo]

Hope the capacitor fix, will do the trick for you as well, my tach worked until I changed the complete dash one year ago...

It probably still works if I remount it.

I'm glad you posted the fix for that. I would have never thought to fix the circuit board and I wouldn't have enjoyed looking for a new tach.

[jtcrespo]

Oh well, looks like I'm in the market for a new tach now. The capacitor fix went fine, but in my neverending inquisitiveness, I pulled the other little circuit board off the top of the housing that turns the needle. Apparently, there are strips of copper(springs maybe?) that are attached to it that I didn't see. Well the spring is now sprung, so the tach doesn't work at all.

Does anyone know of anywhere I can get another tach?

I'll try looking in salvage yards in my area when I get time again.

[Bolder Biker]

This tach problem on the 1983 GS750 is very common........unfortunately, replacement used units are not nearly as common. I got lucky and was given an almost new (only 3 miles on the odometer) gauge cluster by an ex-dealer. Prior to that, I did locate a couple of used units on the internet by doing Google searches, although I didn't buy them.

One thing that I did do while I still had the "wacky tachy" on the bike was to use thin, red pinstripe tape on the speedometer "glass" to indicate redline for each of the first 4 gears. This solved my fear of accidentally over-revving the bike during spirited moments.

BB