1990 KDX200 weak spark (tech help req pretty please)

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1990 KDX200 weak spark (tech help req pretty please)

Post02:05 am May 18 2011

Good Morning gents, I have an ongoing problem with my 1990 kdx 200, whilst out the other week it died :sad: on returning to my workshop i decided it was time for an overhaul! So after testing the ignition system i found the Primary Windings of my HT coil were shorted (0 ohms) I therefore ordered said coil from electrexworld, whilst this was on order i completely stripped the bike and changed the Crank bearings/seals etc (had been a little grumbly previously) after a lengthy rebuild and the arrival of my new coil I expected to be able to just plonk it on and Voila..................Wrong :sad: :sad:

I then decided to test my cdi using the manual for resistance across the different wires but got nothing matching the spec diagram? I therefore stupidly attempted to source another cdi with no joy other than the £114 electrex world. A£114 lighter now and still only a weak spark??? ARRRGGGGHHHHH!!! I have last year changed the iognition stator and the resistance from this is about 176 ohms (which is a bit less than spec but i assumed was ok?(maybe should have said that ealier?

To conclude I have a weak spark and the bike has had a new (ish) ign stator coil, a new ht coil and a new cdi now (and im broke LOL) and still weak spark? Can anyone help me? I have also tried new plug cap/new plug obv

Testing the spark by hand spinning the flywheel with no key in i can get a marginal spark with no plug cap and the lead just to the engine held at a small distance?

Also the new ht coil from electrex has a secondary winding resistance of 9k ohms? is this high cause original was only 5.6k ohms?

Any tech gurus out there wanna help cause im baffled? MAybe the magneto?? :roll: :roll:

Pretty please help me?
kickassuk
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Post02:42 pm May 18 2011

I had the same thing, it was a knackered stator ignition coil.

Things to check -

Are your lights working? This means the rotor is still magnetic thus (hopefully) good
Resistance from output of stator ignition coil to earth, should be between 300 and 500 ohms.
Now measure between earth and the input to the CDI, should read roughly the same as last check (just checking for wire breakage).

If you suspect your CDI is knackered, email this guy http://www.geocities.com/a57ngel/moto/CDI.html he made me a CDI which cost £35 (something like that) it is 4 way adjustable and kicks the shit out of the standard CDI.
moto_psycho
 

Post02:45 pm May 18 2011

It seems very common that the stator ignition coils die on these bikes, and apparently the 1st wave of electrex coils were shit and died rather quickly. I have one of the later ones fitted now and its perfectly fine.

Also, new spark plug. :wink:

Don't expect many of the yanks to help you, they seem more bent on trying to make people feel stupid than actually trying to help them! (no matter how many times you prove them wrong!)
moto_psycho
 

Post03:01 pm May 18 2011

Also the new ht coil from electrex has a secondary winding resistance of 9k ohms? is this high cause original was only 5.6k ohms?


I'd be suspicious of that HT coil. Ask Electrex?
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Post04:36 pm May 19 2011

Well fook me with a cactus it was indeed the Stator coil!!!! I got another new one from electrex n voila! The resistance of this bad boy was like 350 ohms also miles more than the other. Expensive lesson that grr lol. Now i seem to have a slight top end rattle from the top end of the head? Could this be the KIPS rattling maybe since i cleaned it all up??

P.S Thanks alot for your feedback guys it means a lot :razz: :razz:
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Post05:05 pm May 19 2011

If the rattle is apparent at idle, but goes away when you rev it, or gets less when you pull the clutch, that's the kips rattle. If it gets louder when you rev it, then you need to start looking for problems.
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Post12:12 am May 20 2011

>|<>QBB<
kickassuk wrote:Well fook me with a cactus it was indeed the Stator coil!!!! I got another new one from electrex n voila! The resistance of this bad boy was like 350 ohms also miles more than the other. Expensive lesson that grr lol. Now i seem to have a slight top end rattle from the top end of the head? Could this be the KIPS rattling maybe since i cleaned it all up??

P.S Thanks alot for your feedback guys it means a lot :razz: :razz:


Get yourself a CDI from this guy http://www.geocities.com/a57ngel/moto/CDI.html , the electrex coil advances the timing slightly giving you better bottom but worse top, it was £35 delivered to me (took exactly 2 weeks) and is absolutely brilliant!


Info about how the electrex coil affects it http://www.geocities.com/a57ngel/moto/CDI-mod.html READ!!!
moto_psycho
 

Post01:25 pm May 20 2011

worry over noise almost disappears when clutch pressed in? Sure it wasn't as noticeable b4? Mind you i have stripped and cleaned all the carbon out the kips rack n valves like (greased it back up with some molycote grease) It goes like a fatty on a chippendale now! Proper test tomoz,

Moto Psycho Im not buying another cdi just yet Im still crying from the £114 i spent from electrex for this one! :blink: :blink: :blink: :blink:
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Post03:51 pm May 15 2014

Hi
I have , what sounds like, a similar issue (1990 KDX 200) and would appreciate some help.
Very weak spark using BR8ES (can barely see it) but with a B8ES you can make out a stronger spark.
I have tried taking the plug cap off.. And get what looks like a good spark from the HT lead to the head from about 6mm, but its a white spark (have read you should get a strong blue spark). What should it be?
So it might be an issue with the cap (will try locate a replacement today).
However the various ohm readings don't look great either..
The stator coil (r/w wire from magneto) to earth is 234ohms (specs say should be 300-500) but I read you can get away with 20% variance... Is this OK?
The secondary circuit. (HT lead ) to earth is 5800 which is in range (5017-6250), but the primary circuit (tab on ignition coil that goes to the CDI) to earth read 0.6 ohms (range is 0.8-1.2) is this OK?

Any help (and correct me if I've got my terms wrong) would be much appreciated.
Regards
Tim
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Post03:20 pm May 16 2014

Weak spark is usually the coil or HT lead. The signal from the stator to the CDI is just a trigger, the high voltage is generated in the coil. Clean all your connections, make sure your grounds especially are good, replace the coil. You can use a KDX coil or one from a similar era KX
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Post08:10 pm May 27 2014

The stator coil produces the hundreds of volts that the HT coil needs to convert to thousands of volts so it is more than just a "trigger". That 234 ohms indicates there is a partial short in the stator coil and that it needs to be replaced. Just don't get one from Electrex. Partially shorted means it puts out less voltage than it should which means the final spark voltage will be less than normal. Upon reassembly make double sure all the connections between the stator coil and CDI are very good because a loose connection causes the stator coil to short out. It's hard to explain and harder to understand why but it has to do with high voltage generation due to electrical inertia when the normal flow is interrupted due to a bad connection.
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