84 KDX200 power loss

[travisb]

Hello,

I am looking for some troubleshooting help.

I raced my recently acquired 84 KDX200 in a vintage MX race for the first time this past weekend. I was completing laps in about 4 minutes and the temperature was in the mid to high 80s. As I raced, the bike progressively lost power and was more frequently misfiring, perhaps due to an ignition problem (the misfires were accompanied by a pinging sound from the engine). The misfiring was more likely to occur at full throttle.

By the last of 4 laps, the power loss was so severe that I had to use first gear to climb the hills (normally 2nd or 3rd gear).

The symptoms cleared for the start of the second moto, about 3 hours later, but returned just as they appeared in moto 1 after a couple of laps.

I am thinking that coil/stator resistance measurements while the engine is cold might be inconclusive, unless the coil and/or stator are marginal. Maybe I have to ride the bike hard until the symptoms reappear, then make measurements.

Any help would be greatly appreciated.

Thank you,
Ben

[KDX Geoff]

.

Running hot, running lean perhaps...sounds like some pre ignition there that could be from a very hot cylinder running lean and overheating ?

What colour is the ceramic on your spark plug ?

Most of these 200's have been sleeved by now and some have larger bores than standard (my 200 has a 72mm bore and is around 240cc, standard is 66mm) so you might like to pop the head off and check your bore size then you can look at the carb setup.

.

[Jaguar]

look for pitting on the piston and cylinder head.
check the compression to make sure it isn't too high from some previous modification.
check the squish clearance to make sure it isn't too small.
richen the jetting.

[travisb]

Veteran riding friends at the track were convinced that the symptoms were indicative of an ignition problem. (Also, the spark plug was rich and did not have signs of overheating). When I tried to start the bike a week later, there was no spark. The stator source coil and high tension coil resistance measurements were out of spec.

High tension primary=0.5 ohms, vs 0.22 spec; secondary=5.7k ohms vs 7.2k, all specs +/- 20%.

Stator coils:
Blk - blue = 78 (spec=104) ohms
Blk - w/r = 116 (38)
Blue - w/r = 38 (142)
Blk - yellow = 0.5 (0.54)

Edit: spec values in rows 2 and 3 above from the Clymer service manual appear to be incorrect/swapped.

I purchased new stator source coils (no lighting coil), then measured and installed these. According to rmstator, the spec resistance for the large coil is 170 ohms, while the small coil is 24 ohms. The Clymer service manual calls for 104 ohms rather than 170 and 142 ohms rather than 24, so I am not sure these coils are correct for the bike. Rmstator sells these as replacements for 21003-1077, which is the Kawasaki PN for the stator source coils for 1983-1985. Rmstator also lists 21003-1178, which is the source coil PN beginning in 1986, according to microfiche at the Kawasaki.com web site.

I also bought a used high tension coil by mistake (i meant to buy a new aftermarket one).

After installing the stator coils, I had no spark with my original high tension coil. When I installed the replacement used coil, the bike, even when cold, was running as poorly or worse than at the track. When starting, the kick start lever kicks back violently (new symptom) the bike is hard to start (another new symptom), and, once running, back fires and misses constantly, especially at higher RPMs and wider throttle positions (these last symptoms are identical, but more severe than at the track).

I am wondering if I have another combination of out of spec stator and/or high tension coils or if the CDI box could be the culprit. In any event, the source coil resistance measurements are suspect relative to the specs in the Clymer manual.

Thank you for any help,
Ben

[travisb]

Looking at the coil wiring, measurements and specs more closely, I am convinced that the ignition system test specifications, table 1 on page 195 of the Clymer manual are in error. The large coil (Blk - blue) and small coil (blue - w/r) are wired in series. Therefore, it would seem Blk to w/r should be the sum of the two coil resistance specs / measurements (specs: 104+38=142). So, the second and third spec table entries should be reversed, and only the large coil measurement (Blk-blue) of the bike's original coil was out of spec. The rmstator small coil spec at 24 ohms is more than 20% from the Clymer value of 38 ohms, but the coil measurment is within 4 ohms of the new spec interpretation of 38 ohms, so perhaps the rmstator specs are incorrect.

Edit: I should have mentioned that I cleaned all electrical connections with Emory paper and contact cleaner, cleaned the HT coil mounts on the frame and installed a new spark plug. I replaced the source coils with the stator plate on the bike, so the static timing was not changed during the stator coil replacement.

The replacement HT coil fails the secondary test at 3.0k ohms (spec is 7.2k, primary measurement is ok). I installed the original coil and the symptoms persist, although less severe than during previous tests. Next step will be to install a new aftermarket HT coil.

[MCKDX220]

Travis B,

I am going to throw my .02 worth.

Sounds to me like a faulty pick up coil issue (igniter) and or a timing plate adjustment.

The "kickback" typically is indicative of the timing being "to far"advanced.

If the ignition plate is "to far advanced", then you need to retard the ignition, to avoid the kickback.

If the pick up (igniter) is faulty, it just needs to be replaced, nothing you can do about it.

I had a similar problem fixing up my neighbors 95 KTM 250SX.

I could get spark, just not at the right time and moved the ignition plate to the far advanced, far retarded and middle of the settings.

Nothing worked, diagnosis faulty pick up coil, which was also epoxied to the stator, so the whole unit had to be replaced.

(SEM) Comet ignition, not a high quality product.

You now have spark, but is at the right time, doesn't sound like it ???

I would at least trying to remove the flywheel and reset the timing to full retarded position to see if that helps.

If it doesn't, speculating faulty igniter box.

Hope this was of some help.

Michael

[travisb]

Michael,

Thank you for your comments.

The new aftermarket HT coil arrived defective. Primary was ok, but the secondary measured open circuit. I have ordered another replacement HT coil.

I am also suspicious of the large stator coil's measured and spec difference from the Clymers manual. Have not had a meaningful response yet from rmstator to my inquiry.

I want to try replacing the HT coil first, since the symptoms were noticeably less severe with the original HT coil that was closer (but still not compliant with) the Clymers manual. Have to admit that I don't know enough about the CDI to know why the lower, out of spec secondary HT coil resistance would appear like excessive timing advance, but the large stator coil (195 ohms measured vs. 104 Clymers spec) could be contributing as well. If the symptoms still persist, I will get a dial gague to check/set the static timing.

[MCKDX220]

Travis,

One test I did to diagnose the faulty pickup coil was I disconnected the pickup coil leads and same result, spark yes, right time no.

Chasing electrical problems is a Royal PITA, there can be so much speculation and educated guessing until you solve the problem.

Good luck with the replacement HT coil, hope it solves the problem.

Michael

[travisb]

Update - I installed a new aftermarket HT coil and the starting kick back symptoms are gone, the bike idles ok and runs well at low to mid rpm. I need to do more testing, which I can't do at this hour.

I am puzzled by the resistance measurements of this new coil. It reads 0.4 ohms primary and 5.2k ohms secondary, technically out of spec according to the Clymer manual (0.22 ohms, 7.2k ohms). (??)

[travisb]

I am baffled even further after today's testing. The temp/dewPT was 74F/49 today versus 51F/46 last night. I installed a new spark plug cap and new spark plug. The violent kick back symptoms returned and the bike would not start. I installed the original spark plug and plug cap just to rule these out as contributors, but symptoms were unchanged.

I am thinking the stator coils I installed are incorrect for the bike and perhaps the CDI box is intermittent. I still have to check the static timing, but the stator screws were not even loosened during the stator coil swap.

[travisb]

Update...I just finished installing a new pair of stator source coils, measuring 176 and 25 ohms for large and small coil, respectively. The bike started on the second kick and wants to rev out completely. It idles at least when cold and the low end grunt is good, likely improved by jet needle clip setting.

I need to test the bike more thoroughly on trail or track.

Preliminary results implicate the previous set of stator coils from eBay with small coil measured at 34 ohms, more than 20% deviation from nominal. I am hoping the CDI box is ok, especially at higher temperature.