BMW K bikes (Bricks)

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1Back to top Go down   Tachometer Chaos Empty Tachometer Chaos Sun Apr 26, 2015 12:42 pm

Motorbike Mike

Motorbike Mike
Life time member
Life time member
Hi Guys,
I need some help.
I'm modifying a K100,it has 1100 throttle bodies and I'm using 16 valve Motronic ignition,ECU and loom.

I have a Koso RX2N but can't get anywhere with it. The needle waves around wildly and after wiring it in every way Koso advise,I give up. Iv'e tried the RPM signal adapter and that didn't help which is a shame because it would  be a great unit as everything you need is to eye.
So,in the spare parts den I found a Smiths electronic tacho that would have been OK as a temporary unit as I'm
trying to book a track day to do some engine testing-It's had lots done! Obviously a track test is no good without a tachometer so I wire the Smiths unit to find it reads a half engine speed (I think) no matter which way I configure the internal select switches.


Is there some odd technicality of the Motronic tacho signal output I'm unaware of because it seems to affect both instruments?

Gentlemen,I'm in your hands!!

Mike.

    

2Back to top Go down   Tachometer Chaos Empty Re: Tachometer Chaos Sun Apr 26, 2015 11:00 pm

robmack

robmack
Life time member
Life time member
Have you tried to isolate the tach signal feed by using a shielded cable? Select a thin coax or shielded twisted pair. Connect the centre conductor of the coax or one of the twisted pairs between the coil primary and the tach input. Ground the coax shield or the aluminum shield of the shielded twisted pair to the RECEIVING side of the connection, i.e. the speedometer. Don't ground the other side to anything and make the shield cover as much of the signal wire as possible. This might clean up the signal enough for the tach to recognize the pulse transition.

Another possible solution might be to feed the signal through a low pass filter. Try putting a 0.01uF 200V non-polarized capacitor across the tach signal input and ground at the gauge. That should smooth out the signal and give something for the gauge to trigger on.


__________________________________________________
Robert
1987 K75 @k75retro.blogspot.ca
http://k75retro.blogspot.ca/
    

3Back to top Go down   Tachometer Chaos Empty Re: Tachometer Chaos Sun Apr 26, 2015 11:27 pm

KafeRacer

KafeRacer
Silver member
Silver member
I had a similar problem with my dakota digital instruments where the speedometer was going crazy, I had to run a filter on the main power feeding the instruments.  I can't advise on what filter to use, as the one I have my dad salvaged from some old equipment he had.

Cheers.


__________________________________________________
Dave Evans
'Kafe Racer'
kaferacer.wordpress.com

1990 K75RT
1985 K100 Kafe Racer
http://kaferacer.wordpress.com
    

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