KDX 175 1981 hardly any spark

[Thomas G.]

My KDX 175 does'nt start any more.
It has lost its spark at low revs.
It has only a weak spark when you get higher revs. There seems to be a somewhat "cut off rev", when lower the spark disappears.

I have a second KDS 175 in part (unknown if good or bad shape).
I switched all parts step by step.
I went through all wires and checked for any damage - none.
Grounding is checked and good as well.

Here are the OHM-values of the parts:
!! the first digit is from 1.unit / the second from 2.unit
__________________________________________________
Magneto:
blue -> ground -- 150 -- 140 Ohm (blue comes from the smaller coil which I think is the trigger signal???)
red-white -> grnd -- 175 -- 166 Ohm ( this is the bigger coil)

Ignition coil:
green-white -> grnd -- 0 -- 0,6 Ohm
green-white -> Spark wire -- 1800 Ohm -- 11 K-Ohm

Are these values somewhat good or normal ?

CDI :
From my impression I would estimate the CDI to be gone.
Is there any way to check the CDI units?


Any help is highly appreciated.
Thomas

[Jaguar]

I had a '89 Honda CR250 with the same problem. I found some info saying that the magnets in the magneto lose strength over the years and that the only solution was replacing it. Of course being an electronics wiz I made my own electronics solution using seven 9v batteries connecting to the CDIs charge capacitor to make up for the magnetos lack of charge at low RPM.

Go to my page to read about troubleshooting the system: http://www.dragonfly75.com/moto/fixing-ignition.html

I have one adjustable CDI for the KDX in stock if you want it. Just make sure yours doesn't rely on a separate pickup coil for timing trigger. http://www.dragonfly75.com/moto/KDXCDI.html

[Thomas G.]

Hi Jaguar,
I also read about about the magnets losing their force over the years.
No idea how to test this?
I found nothing on the net.
I turned the magneto upside down and the magnet will hold a BIG screwdriver easily.
But is this enough?

I'll try troubleshooting along your guideline.
Your 7x9V solution was putting all in series and giving 60+ V to the capacitor charge input of the CDI?
Am I right?
Thanks,
Thomas

[Jaguar]

yes, all in series through one diode. It worked like a charm and saved me $500 in new parts cost. Here is how I did it although I'm not 100% sure the resistor value is the same. If it works above idle (ie: after push starting) but not at idle then just lower the value to maybe 6.8K:
http://www.dragonfly75.com/moto/images/CDIcharger.gif
Here's the parts from mouser.com : battery clip 121-0424/I-GR diode 512-1N4007 and just buy alkaline batteries locally.

[torgo]

I know this is a year old thread, but how long will 7 - 9VDC batteries last? In terms of run time in hours?

Thx