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RG68RG
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Tachometer is way off (doubles rpm?)
09/12/18 at 09:29:08
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Anyone know a common reason why the tach on this bike would be so wrong? At idle, It appears to be a hair over 2K which isn't correct at all.. Then as you rev to what would be 4K it buries the needle.  It's an 83 Ls and both tach and speedo are in the same panel...  Any help would be appreciated.
  
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Barry
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Re: Tachometer is way off (doubles rpm?)
Reply #1 - 09/12/18 at 11:26:55
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The tacho gets it's input from the ignition coil so basically it counts sparks.  While it's possible the tacho is faulty the first thing I'd do is go through the whole ignition system checking on all connections.
  

Barry Cheshire, England 79 R45
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RG68RG
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Re: Tachometer is way off (doubles rpm?)
Reply #2 - 09/12/18 at 14:40:18
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I'll do that when i get a chance .Thanks!   I was just hoping there was something that is common with this particular bike.
  
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Mrclubike
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Re: Tachometer is way off (doubles rpm?)
Reply #3 - 09/12/18 at 22:22:57
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RG68RG wrote on 09/12/18 at 09:29:08:
Anyone know a common reason why the tach on this bike would be so wrong? At idle, It appears to be a hair over 2K which isn't correct at all.. Then as you rev to what would be 4K it buries the needle.  It's an 83 Ls and both tach and speedo are in the same panel...  Any help would be appreciated. 

What do mean by in the same panel
Do you have the stock tach and speedo or a after market one
If it is after market it may need to be set for  4 cylinder  
  

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RG68RG
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Re: Tachometer is way off (doubles rpm?)
Reply #4 - 09/13/18 at 08:44:16
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No it's stock...the tach just has one multi prong plug and what looks like no adjustment.
  
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Bob_Roller
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Re: Tachometer is way off (doubles rpm?)
Reply #5 - 09/13/18 at 12:31:57
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Here's a link to Snowbums BMW Technical site .

http://www.bmwmotorcycletech.info/tach.htm

It will give you some idea where to look for issues .
  

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RG68RG
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Re: Tachometer is way off (doubles rpm?)
Reply #6 - 09/13/18 at 21:23:19
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Thanks for the link.. been reading it...!
  
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Bob_Roller
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Re: Tachometer is way off (doubles rpm?)
Reply #7 - 09/13/18 at 21:47:48
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It may be easier, to get a replacement tachometer .
  

'81 R65
'82 R65 LS  
'84 R65 LS
'87 Moto Guzzi V65 Lario
'02 R1150R
Riding all year long since 1993 .
I'll give up my R65, when they pry my cold dead hands from the handlebars !!!!!
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RG68RG
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Re: Tachometer is way off (doubles rpm?)
Reply #8 - 09/14/18 at 09:21:31
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I'm starting to think a replacement is probably the answer too..
  
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Re: Tachometer is way off (doubles rpm?)ch of discrete
Reply #9 - 09/14/18 at 10:58:22
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Hello
The tacho is simple. A bunch of discrete components and an integrated circuit to convert the impulse count into a current for the galvanometer.
IMHO, the electrolytic condenser are dead (30 years of harsh conditions take its toll ) and replacing them may solve the problem entirely.
It is cheap and may return the device to it's proper status...
Just my 2˘
  
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RG68RG
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Re: Tachometer is way off (doubles rpm?)ch of discrete
Reply #10 - 09/14/18 at 11:34:21
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georgesgiralt wrote on 09/14/18 at 10:58:22:
Hello
The tacho is simple. A bunch of discrete components and an integrated circuit to convert the impulse count into a current for the galvanometer.
IMHO, the electrolytic condenser are dead (30 years of harsh conditions take its toll ) and replacing them may solve the problem entirely.
It is cheap and may return the device to it's proper status...
Just my 2˘

Where is the (are the) condenser/s at? I have the tach off the bike and on the kitchen table..
  
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georgesgiralt
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Re: Tachometer is way off (doubles rpm?)
Reply #11 - 09/14/18 at 12:42:57
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Remove the screws (and sometimes the color tape) and remove the black plastic cover. You will see the printed circuit board and the indicator bulbs.
On this PCB are  all the components. Change the condensers and try it on the bike.
  
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Re: Tachometer is way off (doubles rpm?)
Reply #12 - 09/14/18 at 14:14:55
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If there is another R65 owner nearby a simple swap of the tacho to another bike would confirm if the fault lies with  tacho or the bikes ignition system.  Actually any airhead would do or even any other twin cylinder machine with wasted spark ignition but that would be more work with the wiring.
  

Barry Cheshire, England 79 R45
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georgesgiralt
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Re: Tachometer is way off (doubles rpm?)
Reply #13 - 09/14/18 at 16:13:23
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You can actually test with a strobo light if you have one displaying the RPM. It should gives you twice the actual RPM if set on 4 stroke engine. (I don't think the strobo maker has though of wasted spark ignition...)
You can also use any electronic tacho for a 4 stroke engine and take it's reading with a pinch of salt given the origin of the tacho.
I do not think the ignition circuit is at fault. if you have points, the tacho just count the number of times the points open per second and divide by 2. If you have an electronic ignition, I doubt the ICU can give a false timing information and still deliver a spark at the right time to the cylinder... But it's just my thinking...
  
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RG68RG
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Re: Tachometer is way off (doubles rpm?)
Reply #14 - 09/14/18 at 19:47:18
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Now I just realized that (tonight)  there are no backlights to illuminate either gauge. the bulb in the speedo is just plain missing (didn't just fall out it's not anywhere to be found) and the ones on the board of the tach just don't work. I looked up a replacement instrument cluster setup on ebay, and they are way too pricey used.. So... Since I don't touch most electrical stuff.. that's probably that.  Last time I had a bike with this much wrong with the electrical...I was 17 and didn't care.
  
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Re: Tachometer is way off (doubles rpm?)
Reply #15 - 09/14/18 at 20:41:16
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I agree with George
More than likely it is a bad capacitor (condenser) inside the tach 
I don't think it is a ignition problem but anything is possible when it comes to electricity   Shocked

If you can solder they are easy  to replace and cheap
  

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Re: Tachometer is way off (doubles rpm?)
Reply #16 - 09/15/18 at 03:13:45
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Well, changing the bulbs in the speedo or tacho is not heart surgery. So i bet you can achieve it.
If I were you, I would buy little led bulbs with the T10 base like the original and install them for general lighting of the instruments. Since I've done that, I can SEE at what speed i'm running at night !
But put plain bulbs in the oil, gen neutral or high beam places or else wear sun glasses all the time, even at night Wink
Look at the bike user manual, all the replacement of these bulbs is explained with pictures. Also, check the fuses. while you're at it.
  
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Re: Tachometer is way off (doubles rpm?)
Reply #17 - 09/16/18 at 17:24:57
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georgesgiralt wrote on 09/15/18 at 03:13:45:
Well, changing the bulbs in the speedo or tacho is not heart surgery. So i bet you can achieve it.
If I were you, I would buy little led bulbs with the T10 base like the original and install them for general lighting of the instruments. Since I've done that, I can SEE at what speed i'm running at night !
But put plain bulbs in the oil, gen neutral or high beam places or else wear sun glasses all the time, even at night Wink
Look at the bike user manual, all the replacement of these bulbs is explained with pictures. Also, check the fuses. while you're at it.


The light for the speedo isn't just missing.. any wires or sockets are as well.. As for the tach? it appears that there are several screwed into the board inside and none work there either.. I'm searching for a fusebox on the bike now as it appears to be strangely hidden...As far as getting bulbs into the non working tach.. I could probably retro fit something in there but the tach still wouldn't work. The only thing it looks like I can practically do, is wire up a light into the speedo. (maybe off the headlight) Which I'm pretty sure is 10mph off. Maybe if I had spent more time with soldering guns and less time with wrenches these last 35 years... Just a thought....Has anyone on this board successfully added an aftermarket speedo/tach combo? Maybe digital??
  
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Mrclubike
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Re: Tachometer is way off (doubles rpm?)
Reply #18 - 09/16/18 at 18:44:28
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Their are only 2 fuses
They should be in a fuse holder that clamps to the top tube at the rear of the fuel tank and directly over the air cleaner

The wires for the  marker lights and instrument lights are Grey/Black
The fuse you are looking for should have a Grey wire coming into it from the ignition switch and a grey/black wire coming out to the lights

Do you have a wiring schematic
  

img514_crHIGH_CON_003.jpg ( 360 KB | 7 Downloads )
img514_crHIGH_CON_003.jpg

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Re: Tachometer is way off (doubles rpm?)
Reply #19 - 09/16/18 at 19:03:55
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We've had members install an Acewell unit, pretty straight forward to install and they seem to be satisfied with it .
  

'81 R65
'82 R65 LS  
'84 R65 LS
'87 Moto Guzzi V65 Lario
'02 R1150R
Riding all year long since 1993 .
I'll give up my R65, when they pry my cold dead hands from the handlebars !!!!!
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Mrclubike
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Re: Tachometer is way off (doubles rpm?)
Reply #20 - 09/16/18 at 19:05:07
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Here is the inst lamp and marker circuit called out in RED
  

coler_schematic_marker_lights.png ( 697 KB | 7 Downloads )
coler_schematic_marker_lights.png

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Re: Tachometer is way off (doubles rpm?)
Reply #21 - 09/16/18 at 20:13:56
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You can also install a Vapor computer if you don't mind homebrewing some mounts.  It's a digital speedo and tach combo.
  

Justin B.

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RG68RG
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Re: Tachometer is way off (doubles rpm?)
Reply #22 - 09/27/18 at 20:45:37
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Was just reading this topic again because I'm installing an electronic speedo/tach.. It's possibly junk but so far everything works except the tach. I've hooked the gauges tach input directly to the existing bikes tach wire with no luck. Wrapped it around the spark plug wire as directed by the instructions and ..no dice.. where else could someone attach one to get a signal?  It's an 83 and I'm not sure if it's electronic ignition yet as I haven't taken the cover off just yet.
  
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Re: Tachometer is way off (doubles rpm?)
Reply #23 - 09/27/18 at 20:48:51
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Starting with bikes produced 9/80 and later, they come from the factory with electronic ignition .
  

'81 R65
'82 R65 LS  
'84 R65 LS
'87 Moto Guzzi V65 Lario
'02 R1150R
Riding all year long since 1993 .
I'll give up my R65, when they pry my cold dead hands from the handlebars !!!!!
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