87 electrical issues - help!

xcracer · Post by **xcracer** » 09:39 pm Jun 20 2013

Fresh rebuild on the motor - http://kdxrider.net/forums/viewtopic.php?f=119&t=14064 - and I can't get it to start.
Found that the lead inside the spark plug boot was cracked, and was effectively disconnected. Replaced it, and now the bike will start, but it sounds like it's not sparking every rev, but every 2 or 3. However often, it's perfectly consistent. Throttle will just bog it and it'll stall, and I have the idle control cranked all the way up (high idle) to get it to idle like this.

Any ideas?
I'm thinking the CDI box might be dead because I tried kicking it (repeatedly - oops) before determining the spark plug boot was dead.

Does anyone know how to repair or build a CDI box for these bikes?
Properly test the CDI box?
I know that there's the "Wolf Pack" design from the Micheal in Ecuador for the newer KDX's, and he also has the part numbers & schematic to build a stock CDI for the newer bikes.
Would my bike work with a newer CDI?
Is it the CDI at all?

Please help!

Thanks

diymirage · Post by **diymirage** » 09:44 pm Jun 20 2013

xcracer wrote:I'm thinking the CDI box might be dead because I tried kicking it (repeatedly - oops) before determining the spark plug boot was dead.

well, you know what they say: if you cant fix it with a hammer, you've got an electrical problem

sorry man, no help

Postigo · Post by **Postigo** » 10:00 pm Jun 20 2013

I don't think is the cdi, check your coil, wiring and grounds. If you replace the rubber boot of the coil take look to the coil side and check if the cable is all the way in got the same problem in the past with a 1981 IT465.

xcracer · Post by **xcracer** » 10:17 pm Jun 20 2013

Postigo wrote:I don't think is the cdi, check your coil, wiring and grounds. If you replace the rubber boot of the coil take look to the coil side and check if the cable is all the way in got the same problem in the past with a 1981 IT465.

Coil resistance checks out good. Spark plug boot is definitely threaded all the way into the cable. (The shop I bought it from warned me about that).
Wiring seems good - going to strip the plastic sheathing and take a closer look this weekend though. Grounds all looked good too.

Only thing I'm not sure of is how to test the wiring to see if it's able to pass full current through it. Resistance testing won't show any problem, even if the wire is cut through almost all the way...

Post by **KDXGarage** » 10:26 pm Jun 20 2013

pull the flywheel, ...check magnets / woodruff key / timing / stator

xcracer · Post by **xcracer** » 10:37 pm Jun 20 2013

Jason wrote:pull the flywheel, ...check magnets / woodruff key / timing / stator

Flywheel - good. Two magnets were re-epoxied when I rebuilt motor.
Woodruff key - good. Sitting where it belongs.
Stator - resistance measures good, appearance is good.
Timing - same as before rebuild. The stator plate was almost notched in place.

Post by **bufftester** » 11:49 pm Jun 20 2013

I'd redo all your grounds, make sure they are good and clean, goes for the remaining connections clean and dielectric grease them. Likely not the CDI if its running at all. It will probably run with a newer unit, but not well. As mentioned above, coil leads at both ends, new plug, fresh gas, clean filter. You can try toying with the timing, but it's a pain to do (did you reglue the magnets because they were broken off, or just as preventive maintenance? They determine your timing and if not exactly right you'll run like ass). If it is running rough make sure your carb is thoroughly clean and set to stock config. You can run a newer coil to help troubleshoot as well.

xcracer · Post by **xcracer** » 06:25 pm Jun 22 2013

bufftester wrote: did you reglue the magnets because they were broken off, or just as preventive maintenance? They determine your timing and if not exactly right you'll run like ass

I reglued them because two broke off when I pulled the flywheel (using the threads to pull, not a gear-style puller).
And this was indeed the problem. One of the magnets was clocked approx 1mm too far back from the tab where it was supposed to sit. The stock epoxy had notches where the flywheel tabs had sat against the magnet, so it was pretty obvious which magnet went where, and when it was seated properly. BUT, I guess I laid down too much JB Weld, which made too thick a layer between the magnet & flywheel, and because of this, the stock epoxy notch actually pushed it further back rather than where it needed to be. I figure I was out 1mm, which would have me at around 1.15 degrees retarded with my timing. (Love knowing how to use CAD).

Pulled it apart, and cleaned up the epoxy, and just as I was prepping to put it back in, I dropped the magnet and it chipped.... NO!!!!!

Does this look like it'll still work ok? Or am I f'ed? (If I remember correctly, the flywheel rotation is counter-clockwise. Which would put this chip on the leading edge).

Post by **bufftester** » 03:51 pm Jun 24 2013

If it is on the leading edge of the magnet then you may be all right. The trigger pulse is generated when the trailing edge of the magnet passes over the sensor if I remember my CDI basics correctly. If you have the chip you could just superglue it back on. If it does turn out to be the leading edge I'd glue it on and see where you're at, all you will have lost is time if it doesn't.

xcracer · Post by **xcracer** » 04:32 pm Jun 24 2013

The chip stabbed me in the finger and was then dropped in the garbage. After that, I realized I might want to glue it back in, but couldn't find it in the garbage bin.... I also did some reading saying that if a magnet is broken in half, they will repel each other at the crack - they can no longer be one continuous magnetic field.

What about flywheel balance? How critical is it? I know I added epoxy, so I probably altered it somehow...?

xcracer · Post by **xcracer** » 08:24 pm Sep 02 2013

So, bike is running.
Finally got it sorted out. Ended up being my flywheel which was giving me issues.

I ended up buying the entire ignition system from GKBO when he decided to abandon his '86 project.
I changed out the CDI, didn't fix it.
Changed the flywheel, and it did fix it.

Still not sure what the issue was with mine, but I noted 4 differences between them.

1 - non-working flywheel had the magnets come loose and JB welded back in
2 - non-working flywheel's taper was magnetic, where the working flywheel wasn't
3 - non-working flywheel had a chip in the middle of the magnet, the working flywheel had a larger chip in the corner
4 - the keyway on the non-working flywheel had a small notch off to the side; which means it might have settled in with bad timing....

I know other people have used JB Weld to put the magnets back in - is this what caused the issue?
I'd like to add some epoxy or JB Weld to the new working flywheel to ensure I don't destroy it, but want to ensure that's not what killed the old one before I go ahead with it.
(I do plan on trying the old flywheel with the timing adjusted, to see if it was the keyway - just not sure when I"ll get around to it. Working on buying an 87 Buick Regal Turbo T soon too, so that might take up some dirtbike time...)

Any input would be great.

Thanks kindly!

Post by **dfeckel** » 07:58 am Sep 03 2013

I used some epoxy on my '83 250 to reinforce the stock magnets. None had broken loose, but the red epoxy the factory used was chipping away easily. I flowed epoxy around all the magnet margins I could access, and everything is holding together well after about 5 hours of running. (I don't ride the bike very often)

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