[JustSomeDude]

Greetings,

I've run into a bit of a snag on an 88 TDub rebuild, and was hoping someone here may be able to steer me in the right direction. I have an 88 TDub that I picked up off of ebay, very rough shape, which I've basically torn apart and rebuilt. I'm to the point of trying to get this thing running but having some trouble getting it started. Compression isn't great (90 PSI cold) but its better than when I bought it and it would start when I got it (which can only mean I've messed "something" up). It does get a very weak spark, and it seems to be getting fuel as well. Every now and then it will 'try' to turn over but, nothing more than a little tease.

So I started going back over the ignition system. Ignition coil (replacement) is within specs on both primary and secondary windings. Pickup coil (green and white wires) is at the high end of spec, but appears ok. The source coil (brown and red wires according to the manual) was WAY out. On the bike, it was reading about 15 Million Ohms. So, I'm thinking probable suspect. However, before I bought a new one I thought I would at least take a look at it to make sure all the connections looked ok....and that's where the question comes in.

I don't see how testing resistance/continuity between the red wire and the brown wire could possibly work....and now I'm wondering if I'm testing the wrong wires.

On the stator, for the ignition circuit there seems to be two coils...a larger one and a smaller one right next to it. My red wire is connected to the larger coil, and the other connection to that coil is a black ground wire that connects to the stator's core. The smaller coil has a brown and yellow wire. However, I don't see how/where there is any continuity between the smaller coil and the larger coil (and thus the brown and red wire) in this configuration....so it would seem impossible for that reading to be within 4-600 Ohms.

I tested the red wire to black wire (as well as to the stator core) and its about 700 Ohms over the larger coil. I tested the brown wire to yellow wire on the smaller coil and it was about 40 ohms. But it is infinite resistance between red/brown or red/yellow. From what I can see, there would have to be some connection to the stator core on the smaller coil for there to be any continuity to the red wire in this configuration....and I don't see anything like that here. Now the harness on this bike was completely butchered....and I wouldn't be surprised if they messed around with the stator as well...because this is just not making any sense to me.

I was hoping someone might be able to confirm the color coding of the wires in regards to what they are connected to on the stator itself, as well as confirm that when testing the source coil, what are you actually testing on the coil itself (for example if what is supposed to be tested is the resistance over the smaller coil....the brown and yellow wires in my particular example....or if you actually are testing resistance between the two coils) I hope that makes sense.

I have pretty much resigned myself to the fact I need a new stator...but after looking at it I'm a little concerned that the color wires listed in the manual (red/brown) don't appear they could possibly be correct on this stator.

Any assistance and/or clarification would be greatly appreciated.

 

[Dubzha]

You mention a brown and yellow wire to a smaller coil. Might that 'brown' wire be a discolored white wire? I'm looking at a diagram, and there are 3 coils, and one coil has a center tap.


The CDI coil has White / Green

The Red / Brown / Black is the large coil, and the Brown is a center tap for that coil. Red / Brown also go to the CDI, and Black is ground.

And the final one, White / Yellow is for the light circuit.

IF, your white wire is as you describe as 'brown', and between the Red wire reads 15 M Ohms, then I believe it. Again, IF it is really the White wire [looks like brown?] That 15 M Ohm reading would flow throgh the ground on the regulator, and to the CDI, and who knows what else.

Check the colors. If they are actually what you describe, Brown / White, then I'm not sure I'm looking at the right diagram.

Hope this helps, and isn't taking you in the wrong direction.

Good luck.

 

[TY80A]

Your stator sounds fine. green to white, red to ground, yellow to brown are the measurements. the coils are pulse, source and rpm in that order off the top of my head. I've asked multiple times and nobody has come up with the actual spec values for those coils but yours are near what mine were and what other yamaha bikes call for.

measure how far your spark will jump to quantify a "weak spark" condition. buy or make your own spark gap jump tool.

possibly welcome to the bad cdi club, sorry

 

[philosobrad]

Just performed the ttr125 Stator/coil/cdi swap on my 88. All in for 40.00...........now if the CDI fries, it's 15.00 on Ebay.


Highly recommended.

 

[TY80A]

Just performed the ttr125 Stator/coil/cdi swap on my 88. All in for 40.00...........now if the CDI fries, it's 15.00 on Ebay.


Highly recommended.

Which 125 did you rob specifically? i tried a ttr125 setup but the foot that holds the source coil onto the ring was vastly different than the TW part. I destroyed it trying to modify it with a dremel so it would fit the tw stator ring. I guess I melted it.

perhaps i had a kickstart ttr125 part and i needed the estart version or vice versa?

 

[philosobrad]

No, you had the same setup. A friend of mine made a new bracket for the source coil.

 

[JustSomeDude]

You mention a brown and yellow wire to a smaller coil. Might that 'brown' wire be a discolored white wire? I'm looking at a diagram, and there are 3 coils, and one coil has a center tap.


The CDI coil has White / Green

The Red / Brown / Black is the large coil, and the Brown is a center tap for that coil. Red / Brown also go to the CDI, and Black is ground.

And the final one, White / Yellow is for the light circuit.

IF, your white wire is as you describe as 'brown', and between the Red wire reads 15 M Ohms, then I believe it. Again, IF it is really the White wire [looks like brown?] That 15 M Ohm reading would flow throgh the ground on the regulator, and to the CDI, and who knows what else.

Check the colors. If they are actually what you describe, Brown / White, then I'm not sure I'm looking at the right diagram.

Hope this helps, and isn't taking you in the wrong direction.

Good luck.

Thanks Dubzha for the reply. The wire is most definitely brown and not white. On my stator, the larger of the two coils just has the red wire and the black (which is grounded to the stator core) and the smaller coil has just the brown and yellow wires. There don't appear to be any 'center taps' that I can tell...which is where the confused set in, as there doesn't appear to be an continuity between the red wire (connected to the larger coil) and the brown wire (connected to the smaller coil). With it completely off the bike I get infinite resistance, and with it on the bike and everything else connected, I'm getting 15 M ohms...so I think you must be right that its going through the CDI and who knows what else.

Your stator sounds fine. green to white, red to ground, yellow to brown are the measurements. the coils are pulse, source and rpm in that order off the top of my head. I've asked multiple times and nobody has come up with the actual spec values for those coils but yours are near what mine were and what other yamaha bikes call for.

measure how far your spark will jump to quantify a "weak spark" condition. buy or make your own spark gap jump tool.

possibly welcome to the bad cdi club, sorry

Thanks TY80A,
Yeah, I think I came across your post and didn't see any answers. If what your saying is correct, then it would suggest the manual would be incorrect in the electrical section as it states the following:

- Disconnect the Pick-up coil leads (Green-White) and source coil leads (Brown - red) from the wire harness. And lists the resistances as:
Pick up coil - 650~790 ohms, source coil 400-450 ohms.

Closest I had to that source coil measurement was the red/black measurement across the larger coil....of about 770 ohm, or thereabouts. I suppose its completely possible this guide is just wrong and these wires/measurements are not accurate to this bike. I was hoping to get a better understanding of what exactly should be getting measured, regardless of wire color, and go from there.

I do intend to try the spark gap tool to verify if the spark I'm seeing should be strong enough to jump the gap under compression.

Thanks again

 

[TY80A]

Yes the manual is written for a 1987 bike which is the only year with that specific stator and its resistance values. The stator was changed in 88 but the manual skips all the bikes from 88-2000 and then covers the 2001 and later in the 'supplement". way to go yamaha.