125-200cc Humiliating Loss of Spark--'08 CR125

Sunday's pleasure ride in the NJ Pines ended in a humiliating 5-mile tow from my buddy's KTM. After 30 or so miles of whoops and fire cuts, we were working our way back to the truck on a choppy Jeep trail. I was motoring happily in third or fourth at a low-ish speed, and the engine just quit--no rough running leading up to it, no sluggishness, no cutting in or out. It just died as if I were holding the kill switch.

Trailside checks failed to turn up anything:

Plenty of fuel, plenty of flow.
No spark.
Plug not particularly fouled looking (a little wet from kicking with no spark).
No obvious bad connections.

We even tried a new plug, but still no spark.

Luckily, my buddy brought his tow strap. Unluckily, he was on a KTM.

I spent the last four hours in the garage troubleshooting the problem with little luck. My first thought was my homebrewed KTM stator had a bad connection in one of the wire splices, so I pulled it apart and resoldered all the joints. No go.

I completely disconnected my headlight and Moose wiring harness, and I reconnected the stock kill switch. No love.

At this point, I'm thinking either the coil or the ignition black box, and I'm calling on all the 125 gurus (Norman, Kelly, Bluehusky144, et al) for a guess as to which one it is.

Here's a little more background information. The bike had been getting hard to start the last couple of rides, requiring a collosal kick and a lot of throttle to start. I was thinking it was just a jetting issue, but now I'm not so sure. At my last enduro, it stalled unexpectedly at low speed several times. I had chalked it up to the 2500 foot altitude and my sea-level jetting (390 main, 30 pilot, 60 needle middle clip, 1 1/2 turns) resulting in plug fouling. A little plug cleaning got it going again at the enduro. But again, now I'm not so sure it wasn't an intermittant spark problem. Except for the hard starting and sporadic stalls, it was running beautifully right up until it quit.

Sorry for the long-winded description.

Please chime in--coil, black box, other?

Thanks!

I would start by tracing the wires from the pulse generator under the cover to the ignition black box(control unit)....and make sure your getting a trigger when you crank it over at the black box connector....after that... the coil is pretty easy to check...primary and secondary.....check terminals when disconnected....across the spade terminals for primary check(around 1 ohm)..then from one of the primary terminals to the plug wire( 8- 15k ohms)

make sure the kill switch isnt shorted....by disconnecting it

if it all appears ok then then the control unit is at fault.....

I can check mine if you need more info......

Can you walk me through how to check the coil? I didn't follow. Primary? Secondary?

Oh, I forgot to mention. I had a new pulse generator--I didn't know what it was called until you mentioned it--and I installed it when redoing all my connections.

Yes I can.....but I should wait till I am at home and I can lift the tank off mine....then I can be a better guide....

there should be two wires into the coil....and one large one coming out(plug wire)
disconnect all three....measure across the smaller ones(primary)

then from anyone of the smaller ones to the end of the plug wire....(sec)

Am I measuring resistance? Continuity?

yes....let me get back to you by PM later

I know....

the boss left early.....

I think I've heard Fran Bottone mention that CR125's can have an ignition problem, when the plug lead is routed too close to the coil. Some kind of electrical interference happens.

Norman, I read that too before I bought the bike, so I rerouted the plug wire first thing. Thanks for your 2 cents!

First thing i thought of was this is the guy with the KTM parts on his bike
Did it come loose and get out of time do you have your stock stator to plug back in
Is a moose stator as good as a stock one
just thinking out loud But i would try going back to the stock stator to see

Aren't those bikes cheap enough when they break or the oil is dirty you just buy a new one? Just kidding, sounds like a stator that was going bad with the hard starting/weak spark before but I am guessing. Some of the older ones people swore the spark plug boot was causing issues.

ok there are 4 wires coming out of the ignition cover....2 provide current for the coil...and the other two provide trigger for when the spark needs to occur.....

first ...ohm out the black/yellow wire in the b box connector to the frame....it should not be grounded(open)..thats the kill wire... check that first.....

you need to tell me at the b box connector what the 4 colors of the wires are....there are two different examples......these are coming from the under the IG cover in the harness

yours should be blk/red...red/wht...solid red and solid green


I will check mine tommorow for readings if you need me to.....


I agree with ajax and I would swap in the oem parts at least temp till you get this sorted...at least for now


mine has always been hard to start cold....20 kicks sometimes....it needs a larger starter jet.....I wouldnt go by that yet as IG trouble....

Yes the CR dave.....WR starts first kick

Picked up a multimeter today, I'll post up my findings tonight/tomorrow.

start with this....

across the red/ blk wire and red/ white measure ohms with the connector disconnected at the b box you should have...roughly 25 ohms..if you do..switch meter to AC volts and while cranking the engine by hand and watching meter it will throw out volts 5 to 10V..this is your stator output..

then measure in ohms across the red and green wire with connector disconnected....this will be about 96ohms...this is the pulse generator...there is a little square slug of metal on the flywheel that interupts the voltage ..if resistance is ok..switch meter to m/v and crank engine fast with the kicker with your hand....its in the neighborhood of 150-250 m/v...the B box fires a reference voltage down this line...and the slug of metal produces a square wave signal...seeing as you cant check this because it wont run....checking the inductive output is all you can do for now.....

if this all checks out ok...then the B box is probably fried....



also.....you can also check every wire to grnd to verify no short to grnd.....could also be your problem

and.......have you checked to make sure there is no GRD on the yel/blk wire???

It's not too hard to throw the stocker back in, but it's cutty, splicy, solder, shrink tube, and I take forever at that. I'll do a little more investigation with the coil and if it gets me nowhere, I'll throw the stocker back in.

the coil primary and secondary is also measured from the B box connector as well......as long as the connector is disconnected.....and you dont have to pull the tank...these specs are right off my 06 CR.....


Blk/wht wire to ground is primary resistance...... .4 ohms this will vary with temp but not by much

then measure the same Blk/wht wire to the end of the unplugged spark plug lead...this is secondary....and its about 10-12000 ohms(make sure you change the scale for this measurement 40k )