kdx250 sparking issue

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HondaGuru
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kdx250 sparking issue

Post by HondaGuru »

I got a 1981 kdx250 given to me. I mechanic for a living but mainly 4stroke and street bikes.
Well it makes great compression I cleaned and set up carb like I do anything else. Gave her two kicks fired right up idled just fine on choke. Ran for 1-15 seconds and died. Played around fiddeling with it and no spark.
So out come multimeter. Test stator output voltage to yellow wire from stator 13-19V depending how hard hand kicking with no plug in. I tested power to coil green/white wire and getting up to 13-20v and all power dies when hits coil. Nothing comes out. So I have three other coils tested them same deal. I cleaned stator pick ups with emory cloth now nice and shiney no more rust. That gave me more power thru cdi and to coil. Before was a little weak but it fired right up. Then died.
I have tested Nd tested ohming wires grounds etc all I can think of.

For the life of me I dunno whats goin on why no voltage coming out of coil. Plenty power going in. Now remember I tested three different coils. Even tried different cdi box.
I'm using ngkB8re? Plug.


HELP PLEASE!
pumpguy
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kdx250 sparking issue

Post by pumpguy »

Are you sure you have a good ground connection from the coil to the frame?
HondaGuru
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Re: kdx250 sparking issue

Post by HondaGuru »

The ground to coil is supplied from cdi and has good resistance. Even put star washer betweens coil and frame just incase it needs ground itsself out.
everybody has said ground ground grounds and I have checked all. Even ohmed it all out.

Any other test I should know about? Are my #s good from stator and to coil from cdi?
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bufftester
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Re: kdx250 sparking issue

Post by bufftester »

If you're sure all your grounds and other connections are good try the following.

Ignition coil primary winding resistance, check from the green/white wire to ground (disconnect the wire from the CDI first) should be in the range of 0.16 - 0.24 Ohms
Ignition coil secondary winding resistance, check from the spark plug boot to the ground on the coil, should be in the range of 5,000 - 7,600 Ohms
The only good way to check the coils is with a dynamic coil tester, most of your shops have them. the 3 needle arc distance should be 6mm

Sounds like maybe there is a break in the plug lead to the spark plug if I had to guess blind, or the coil is not grounded sufficiently. There should be a separate ground wire on the coil that mounts to the frame under the coil bolt.
HondaGuru
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Re: kdx250 sparking issue

Post by HondaGuru »

Yes has the separate ground wire to coil. All surfaces are shiney. Got good ground frame engine coil.
Coil primary winding resistance is okay. Secondary winding couldn't get good number.
and iv tested 2 other coils other than one came on bike. Most coils are created pretty similar iv sealed them time to time for test and emergency situations. I know my other two coils work. Maybe twostroke coil is a little different? ? Like I said in into I do thumpers not smokers.
but this bike was free :)

Ill try upload pic here in bit
HondaGuru
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Re: kdx250 sparking issue

Post by HondaGuru »

Here's a picture of the old thang!
Image

Please more help! Ill send a dirty picture afte a ride if I get it going.
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bufftester
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Re: kdx250 sparking issue

Post by bufftester »

Were the other 2 coils you checked from a 2 stroke or a 4 stroke? Seems like I remember there being a difference between them. If you have voltage going from the CDI to the coil then you have a bad coil or plug wire. You might be able to use a CDI/coil from a later (91-94) 250 in a pinch.
Dekon
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kdx250 sparking issue

Post by Dekon »

Have you tried a new spark plug?
dfeckel
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kdx250 sparking issue

Post by dfeckel »

Here is an idea from my wealth of electrical theory ignorance, but these old air-cooled KDXs have 6-volt lighting setups. Would this mean any replacement coil also has to be of the 6-volt variety to work? Something is telling me that shouldn't matter, but it's easy to forget these antique-y enduros have 6-volt systems.
David Eckel
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kdx250 sparking issue

Post by dfeckel »

This may also be useless background noise, but I'll post up the electrical testing page from my 1983 KDX250 manual.

Stator Coil REsistance
Exciter Coil (meter setting R x 100) White/Red to Black 126-190 Ohms
Signal Coil (meter setting R x 10) White/Red to Blue 25-37 Ohms
Lighting Coil (meter setting R x 1) Ground to Yellow 0.31-0.46 Ohms

Ignition Coil REsistance
Primary Winding (meter setting R x 10) Ground to Green/White 0.50-0.76 Ohms
Secondary Winding (meter setting R x 1000) Ground to spark plug lead 1.4-2.1K Ohms

There is also a table on how to test the CDI

Image

Hope this helps!
David Eckel
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kdx250 sparking issue

Post by HondaGuru »

:bravo: Wow thanks for all the replies and info. :bravo:

Yes the coils I used were from a four stroke. I thought about the 12v 6v difference in coils, but saw my number in 12-20v so thought maybe it was 12v. But being 81 I know a lot things were 6v operate. I dunno.
So are coils really different from two and four stroke??? It was a thought when I was trying it.
Ill get out there tomorrow and try some more test before I start replacing everything///

Its I pretty clean bike I think once I washed all the dust and webs off. But its all here. And ran when put away. Kid almost hurt himself 5-10 years ago. They did new top end on it. See use of silicone.. which makes me wanna pull it apart and replace it. But has great compression and has ran for me 1hr after I got it home. Darn tires are kinda new and hold air. Can't believe it..

Ill try figure it out, tomorrow. I went and rode my built CBR 900rr tonight :twisted:

Thanks again ill be back hopefully with a dirty pic of fixed bike or some news. :hmm:
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kdx250 sparking issue

Post by HondaGuru »

Okay sorry guys got lost here for a while no time for the ol KDX...
Here's the #s from stator and coil testing
Red/white to ground .265 ohm at 20k I don't have. 10r
white/red to blue is 25.7 ohm at 20k
ground to yellow .76 ohm at 20k

Ground to green/white .7 ohm at 20k
ground to spark plug lead 5.56ohm at 200k

Everything seemed okay except for the 5.56 ohm that like 4times amount of resistance that's standard?
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bufftester
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Re: kdx250 sparking issue

Post by bufftester »

is it 5.56 ohms, or 5,560 ohms (5.56k)? 5.56ohms is a shorted secondary winding in the coil, which would cause no spark.
HondaGuru
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Re: kdx250 sparking issue

Post by HondaGuru »

Think I found the problem. I saw Lil indention on the ignition coil wrap so I peeled off the insulation wrap and saw two or 3 wire that had been barely knicked. I imagine it was just enough to cause issues.
I also went ahead and rep wrapped the lighting coil with new 18awg polyimide magnet wire since I could see visible blackish burns in coating on wire. Searching for the tiny angel hair for other coil. The coil had a real weird winding pattern hope I get it back right.
Should have the stuff this week to finish wrapping it up.

Do they remake the coils for these bikes?

Iv rewrapped stator chargeing coils before without fail. So I'm gonna try the ignition coil :)
Wire is cheaper than replacement part id imagine ..

But if anybody has a known good part let me kno I maybe intrested! :)

Sorry iv been busy with life and the dirtbike has taken spot in corner till other day. But shell get fixed Nd ill share what I did maybe some pics of coils after rewrap.
HondaGuru
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kdx250 sparking issue

Post by HondaGuru »

Hey guys. I got my wire and rewraped the ignitor coil winding. Still havering problems. My voltage out of wires is inconsistent one kick it'll read 4.5v etc and another will show zero or very low then it'll show high again. This thing is irritating.
Has anyone here rewound their own ignition windings? And do these flywheels go bad?
I'm bout at wits end and its bout to get a new shiney for sale sign and pushed to the road! :(
Id love to get this ol gal going again. Its ran once the first day i got it. But after 8-10 secs it never sparked again..

Anyone with some help would be greatly appreciated
Btw we just got 6inchs of rain would be great to play in the mud and trails :)
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