Project: Dual lighting coil SR stator into US KDX200

[TheRadBaron]

I'm in the process of plating my US-spec '89 KDX200. I'll be installing a Baja Designs dual sport lighting kit and I've been exploring ways to get more power from the stock stator. Rewinding the stock lighting coil has been covered here in great detail, and there are a few aftermarket options to get more juice. I had been planning to rewind mine but then I learned about the SR-series KDXs that were sold in foreign markets and came with dual lighting coils. I searched around a lot for information about these but aside from a few pictures I didn't find much. The thinking was that if you were able to find one it would swap right into a US-spec KDX and give you lots of wattage. The problem is that they're very hard to find.

Well, I found one. I picked it up from the Post Office today and just got it home. I fear that it's not going to be as direct a swap as we had hoped, but I'll get to that in a minute. My goal here is to figure this situation out and document the whole process so that the information will be out there and hopefully helpful to the KDX community. My initial impression is that this is a project that will benefit from having a number of guys who know their stuff thinking about it. I know that there's a lot of interest in getting more lighting power out of our bikes. As a side note, I was reading through the Baja Designs literature about their Dual Sport Lighting Kits and they say that they make a special lighting coil for the KDX that puts out 120 watts. That sounds very interesting. I haven't looked into that any further but that could be very cool.

Back to the SR stator. I'm just focusing on the mechanical aspects before I get into the electrical aspects. Here are a few pictures of the SR stator compared to a US-spec stator. The biggest difference other other than the number of coils is that the ignition source coils are 180 degrees apart. I consider myself a pretty good 2-stroke mechanic but this brought up a glaring lack of knowledge about how an ignition like this triggers the spark. I know the source coil provides the energy to fire the ignition but I don't know what triggers the ignition event in a CDI ignition. This could be a serious problem if the triggering mechanism is also 180 degrees out. I need to figure out whether or not this is the case before I start trying too hard to solve it. If so, the first things that come to mind are to find an SR flywheel or to have a keyway cut into the US flywheel 180 degrees from the original one. That should locate it properly. But maybe I'm getting ahead of myself.

The second potential problem is that the lighting coils are taller on the SR stator. I'm not sure whether or not it would fit under the US flywheel. I'll start looking into that one in the coming days. This might not be a really fast-moving project since I have a lot of other stuff going on, but I wanted to get the ball rolling. Hopefully some of you guys can chip in with some insight.

[bufftester]

The igintion issue using the SR stator plate and the KDX flywheel would have to be resolved as you mention, but the non-starter may be the height of the SR coils. IIRC there isn't a lot of room under the KDX flywheel. ANother route that I have thought about but have never gotten around to trying is to modify the KDX stator plate to accept a second lighting coil in series with the first one. Then there is no change to the wiring coming out of the stator. That is how the SR stator plate is wired I believe (the two lighting coils in series). It shouldnt' be too difficult to mount the second lighting coil in the space on the plate. My crude graphic rendering follows:

This is the stock KDX plate, with the yellow lead running from the lighting coil on one side up to the light switch and the other side of the coil grounded to the stator plate


This is my idea of a modified plate, with the yellow lead still running from one side of the first coil, but the other side would be ungrounded from the stator plate and soldered to the input of the second coil (where the yellow wire would come out from normally) and the other side of the second coil grounded to the plate.


The benefit would be that you could run much thicker guage windings (for more current) and still generate enough voltage to drive everything (as you know the gauge of the winding wire determines the current, or amperage, and the number of turns determines the voltage. On a single coil setup you can go thicker wire to get more current, but at the expense of a lower voltage which keeps you from using too much thicker than stock and still powering lights. But with a second coil in series the voltages would add, so you could run very thick gauge that would only give say 8 V, but do it twice so you get mega current at 16 V) Of course it's all theory and conjecture and I've yet to try it, but if someone else wants to give it a go we'd all be waiting on pins and needles!

[chkdx]

I wouldn't worry about the ignition source coil being 180 degrees off. I tested my H model ignition with an oscilloscope ( I used to design aftermarket car ignitions and was curious ) and found that the spark plug sparks twice per crankshaft revolution! Once at the normal time near TDC and again 180 degrees of crank rotation later, near BDC. Odd, but true.

So, if your ignition source coil is 180 degrees off, but the ignition makes a spark every 180 degrees of crank rotation, your engine won't know the difference.

I really doubt your stock KDX flywheel is going to fit over that SR stator assembly though. Probably have to find an SR flywheel.

[bufftester]

That's an interesting observation about the dual sparks. Also, one of our members in his SuperMoto build went through some of this check it out here http://www.kdxrider.net/forums/viewtopi ... el#p156870

[TheRadBaron]

Hmmm. I really thought that I was blazing a trail here but it seems that dude541 already did a lot of the heavy lifting. I wonder why I never found that thread when I was searching. Very cool stuff that he did. I sent him a PM to pick his brain about a few things so hopefully he can shed some light.
That's some really interesting and helpful info you guys have posted. The twin spark thing gives me hope that maybe, just maybe, the original flywheel can be reused. I know that's a common thing in 4-strokes, so-called "wasted spark" ignition, but I wasn't aware that it was used in 2-strokes as well.
I'm also waiting to hear back from a guy who says that he has an SR flywheel that he'll measure for me. Maybe I can glean from that whether the two flywheels are dimensionally the same or not.

[newbbewb]

I wouldn't worry about the ignition source coil being 180 degrees off. I tested my H model ignition with an oscilloscope ( I used to design aftermarket car ignitions and was curious ) and found that the spark plug sparks twice per crankshaft revolution! Once at the normal time near TDC and again 180 degrees of crank rotation later, near BDC. Odd, but true.

So, if your ignition source coil is 180 degrees off, but the ignition makes a spark every 180 degrees of crank rotation, your engine won't know the difference.

I really doubt your stock KDX flywheel is going to fit over that SR stator assembly though. Probably have to find an SR flywheel.

pardon my possible ignorance, but wouldn't the coil phase being off mess with the static ignition timing? you say NEAR BDC, which if flipped backwards would be NEAR TDC.

[TheRadBaron]

It certainly could totally mess up the timing. However, chkdx says that the ignition fires the plug twice every revolution, 180 degrees apart. Firing the plug near TDC and near BCD every revolution. If this is true, it could mean that having the source coil (and presumably the trigger) 180 degrees off from the original position would not make any difference in the ignition.

[TheRadBaron]

Or maybe I misunderstood your question. You mentioned static timing. I take that to mean checking the timing with the motor not running. If you mean lining up the timing marks you might be right. I plan to take a lot of time to verify the proper ignition timing both before and after I modify anything. Since I don't think that you can really static time a CDI, I'll probably use a timing light, TDC indicator, reference marks, digital tachometer, etc.

[chkdx]

pardon my possible ignorance, but wouldn't the coil phase being off mess with the static ignition timing? you say NEAR BDC, which if flipped backwards would be NEAR TDC.

I'll be more specific. Let's say that the ignition normally sparks 10 degrees before TDC. When it makes another spark 180 degrees later, that spark, by definition, occurs 10 degrees before BDC. If the source coil is then relocated 180 degrees on the stator plate with no other changes, then the spark that used to occur at 10 degrees before BDC now occurs 10 degrees before TDC. The engine doesn't know the difference; a spark at the right time is still a spark.

As the OP noted, this "extra" spark that occurs is commonly known as a "waste spark" in the automotive world, and is normally done to simplify the ignition circuitry.

Now, the timing marks on the SR stator plate may well be in a different location in relation to the mounting screws, compared to a normal KDX stator plate. If so, then yes, static timing will be different. There's also a good chance that the SR flywheel's magnets are in a different location compared to the normal KDX flywheel, which will also affect timing.

All this means that it's probably best, if changing to the SR stator plate, to also change to the SR flywheel to keep the timing correct. In that case, follow the SR service manual for setting static timing.

And FINALLY, this all assumes the normal KDX CDI box is compatible with the SR source coil and flywheel. I don't know, but it seems like another member here (Jaguar?) has found that the SR and KDX CDI's are identical.

[newbbewb]

Great thread. Thanks!

[newbbewb]

Maybe I can glean from that whether the two flywheels are dimensionally the same or not.

yes, do let us know. I'm out of wattage after 35w HID and LED helmet lights. very interested in this. Thanks!

[TheRadBaron]

I heard back from the guy with the SR flywheel and I have a whole bunch of measurements to compare now. I just got called out of town for a few days so it will be a while before I can get back into my shop and compare.
I'm also communicating with Baja Designs to see if I can get any information about this 120 watt KDX lighting coil that they offer, or at least used to offer, or at least thought they offered. If it indeed exists that could be another cool option.

[TheRadBaron]

I have some interesting news. A few of the Kawasaki dealers in New Zealand that I contacted got back to me about the SR flywheel part number. One even sent me a PDF of the parts fiche view of the generator assembly. The part number for the SR flywheel is 21007-1177. This is the same part number as the US-spec E-series KDX. I suppose it's possible that Kawasaki used the same part number for different parts in different markets but this seems highly unlikely to me. This gives me some real hope that the flywheels between the SR and US-spec models are identical. I'm still out of town but I'll post up the PDF when I get home.

[bufftester]

Now that would be interesting, though it's not getting much easier to find E-series parts either. Still scratching my head over the purported wasted spark arrangement, not entirely sure why they would have designed that into a single cylinder bike. Eagerly awaiting updates.

[TheRadBaron]

I've been mulling over the wasted spark arrangement, too. It makes perfect sense from a practical engineering standpoint on a 4-stroke but it doesn't seem like that would be the case on a 2-stroke. One idea that occurred to me is that it possibly could reduce plug fouling. Having the plug fire again near BDC could help burn deposits off the plug. I'm just kind of reaching for ideas, though.

[bufftester]

Yeah, the problem I see with firing the plug near BDC is that the transfer ports are open in prep for the fuel charge and there is a possibility you could in theory ignite ambient fuel in the bottom end of the motor (there is always some fuel there along with the 2T oil) On a 4 cylinder bike you place the cylinders so that the opposite firing pairs are 180 out and then just spark every revolution, makes CDI design so much simpler, but on a 2T single just don't see it, If that is the case then your actually doubling the wear on the CDI and ignition circuit for no reason whatsoever....may have to dig out my oscope and timing light this weekend.

[TheRadBaron]

Yeah, the transfer port/blow up the bottom end thing occurred to me, too. Very strange. That would be great if you could dig the diagnostic stuff and try to get some answers. I won't be able to get to mine for a while and I don't have an oscilloscope. I was planning on making timing marks on my motor and using a timing light to try to figure out some things. I figure I'll find TDC using a TDC finder. I'd make a static timing mark on the motor and one on the rotor to correspond to it. I plan to look up the factory timing specs and make another mark on the flywheel for the proper timing at idle, and another mark for the final timing. Then I could make some corresponding marks on the flywheel 180 degrees apart (BDC). If I shoot the flywheel with light with the motor running I should be able to tell if another spark is happening at or near BDC. Am I on the right track here?
That's of course a pretty simple test and I'd do some more detailed testing before I concluded that everything is as is should be.

[chkdx]

I thought the same thing and first noticed the waste spark on mine when checking the timing with a timing light; it didn't look right and seemed to be flashing very fast for the bike being at idle. That's when I hooked up an 'scope and found that, if it were only doing one spark per revolution, then it was idling at 4000 rpm -- which it wasn't, I could tell by the sound. It was idling normally, which would be more like 2000 rpm. Only answer was it was sparking twice per revolution.

With the timing light, the marks looked "washed out" and dim, which makes sense, because half the time the light was flashing on the side of the flywheel without marks.

[Roadhazardguy]

I started modifying a Kawasaki G4 stator to fit my kdx, I still haven't made any progress since I last posted but it's similar to what you're doing. http://www.kdxrider.net/forums/viewtopi ... 33&start=0

[adam728]

Not sure on the KDX waste spark thing, but on 2 stroke twins it is pretty much standard thay both plugs fire at the same time, so there is a near TDC and near BDC fire on each cylinder. Snowmobiles, Banshees, old Yamaha RD's etc mostly are setup this way. There's still not enough mixture up in the head/plug area to light off.