Weird tach behavior

[Macmatic]

I was riding a couple of days ago when I experienced some weirdness with my tach. I'm thinking its probably the tach itself, here is what happened.

I was riding along the highway trying to get some ideas about my flat spot at around 6,500 rpm and low power when rolling on in 5th at around 5k rpm. What I was doing was riding in 2nd and going to WOT quickly. Previously I'd feel a deceleration followed by strong acceleration most of the time when doing this but at that time I had my needles all the way raised and on this ride I'd put them back to the middle position. NOW what I'm seeing is the tach needle rising from 6k to around 6,500 and then falling quickly below 6k and rising again. This is not marked by a change in acceleration when the tach is dropping so I think I'm not really losing spark = must be the tach. Right?

I have another tach and an ignition box, I also just bought coils off an '05 Katana so want to figure the tach out and then try the other ignition box to see if it helps with the flat spot.

Any ideas tips?
/\/\ac

[kichigai]

Well, I can relate! I too have very simular symtoms as you on my bike. I think it started after my bike fell off of the kickstand. I have read that this is kind of a common problem. Some have added or change a resister in the gauges to resolved the problem temporarly but never read anyone ever solving the problem completely.

[catbed]

i have noticed my tach bouncing around when there is a load on the engine. the tach works fine with no load.

[Macmatic]

I searched some last night but didn't find any of the threads that have covered this in the past. I'm going to drop in my other ignition box today and see if it runs any differently or changes the tach behavior.

/\/\ac

[kichigai]

Check out the post below on this topic.

http://www.thegsresources.com/_forum/showthread.php?t=65806&highlight=bouncing+tach

Or under search, try looking up Bouncing Tach.

http://www.thegsresources.com/_forum/search.php?searchid=696036

[flyingace]

The tach has a delicate electro-magnetic mechanism inside that drives the needle. Once it goes, it's gone. I know - mine started to bounce around, and I could not cure it. A new cable didn't help, taking it apart didn't help. I ended up with an ugly new JC Whitney tach (or 'tack' if you will) that has simply worked great for the last 8K miles.

You can try a new cable (might work), take it apart and try to fix yourself (not easy) or send it to one of those old tach speciailists (have lots of $ ready) or just replace it and live with ugly.

[Macmatic]

The tach has a delicate electro-magnetic mechanism inside that drives the needle. Once it goes, it's gone. I know - mine started to bounce around, and I could not cure it. A new cable didn't help, taking it apart didn't help. I ended up with an ugly new JC Whitney tach (or 'tack' if you will) that has simply worked great for the last 8K miles.

You can try a new cable (might work), take it apart and try to fix yourself (not easy) or send it to one of those old tach speciailists (have lots of $ ready) or just replace it and live with ugly.

Does this apply yo mechanical and electronic tachs? Mine is electronic... are the cable driven ones all mechanical like a speedometer or does the cable drive a signal generator in the tach housing?

/\/\ac

[teh_engr]

Could this be a slipping clutch instead of a tach error?

[gs scott]

What happens if you just roll the throttle open? Good throttle control and all that...

[Clone]

Welcome to the club, that of the failing electronic tach, once it starts to fail it is tough to get it to work well. I have had mine apart twice and replaced all the electronic componets on the circuit board except the super secret black chip in the middle. It works better for a time, but then starts a steady decline. I have decided that the problem is more related to the actual brass mechanism and unless you can score a new one I think you are just going to have to deal having an inaccurate tach.

[flyingace]

Does this apply yo mechanical and electronic tachs? Mine is electronic... are the cable driven ones all mechanical like a speedometer or does the cable drive a signal generator in the tach housing?

/\/\ac

Of course not - sorry - I assumed you were referring to the stock tach because I've never heard of an electronic tach 'bouncing'.

[catbed]

i dont use my tach when im riding at all anyway. i go by feel and sound.

[hcritz]

I had the floating tach syndrome on my 1150...I did the capacitor replcement and lubed the mechanical bits with some lightweight teflon lube...and it's working well so far.
It's not too hard to do on the 1150...

[Macmatic]

What happens if you just roll the throttle open? Good throttle control and all that...

Heh. I have no idea.....

I very rarely snap the throttle open like that but last weekend I was trying to figure out a flat spot at around the same rpm range. Usually I get what I'm looking for with a lot less wrist! Anyway the flat spot turned out to be caused by having my needles raised too high, returned those to normal and the flat spot went away.

I first noticed this tach problem when I was testing on the carbs and the tach is acting just the same now that I've gotten rid of the flat spot. I also tried my backup ignition box with no change to the tach. The bike did seem to feel a little more powerful but not more than wishful thinking would account for. I'll try and do some testing between them later.

Could this be a slipping clutch instead of a tach error?

No, I don't think so. The engine sounds like its climbing at a normal rate and "feels right". Also the tach is dropping and then rising to around where it should be. This seems to happen between 6 and 7,000 rpm. By 7k or so its caught up and holds steady at what seems like about the right rpm. I don't really trust it around redline now though...

/\/\ac

[Macmatic]

i dont use my tach when im riding at all anyway. i go by feel and sound.

Yeah, I don't really use it when I'm just riding either but I had a flat spot at a specific rpm I was trying to diagnose when I noticed the weird needle movement for the first time. Pretty much the only times I look at it are when I'm messing with the choke or getting close to redline.

/\/\ac