I know some of you fellows out there are still repairing ATVs ( as I am ) and may have seen the issue I'm about to describe.
One of my customers has brought me a 2005 Bayou 300 to repair, say's sometimes it runs....sometimes it doesn't.... I have found the issue to be intermitant spark ( which truly sux... ). I don't like throwing parts at anything, but not sure what to do on this one.
- Coil, secondary, primary, boot...all check good ( and I have actually never
experienced a faulty coil on a Jap bike )
- CDI voltage measurements are good
- Kill switch...good
- Found damaged wired to pulser coil...soldered/heat shrank, good
- Pulser coil resistance...good, 430 ohms
- Stator, resistance ....good
Again, I'm not about wasting someones money by throwing parts at it but this particular ATV may be the exception to my rule. Since the pulse coil wiring was damaged, I'm leaning in the area of replacing it ( tho it measures perfectly ). Other reasons, in my experience ( about 30 years of part time repair....dirt bikes as well ) I have never seen a CDI failure that was intermitant, nor have I seen this with a stator.
So, long story short, I could use some opinions on what might be the most probable cause of the intermitant spark. Did I state how I "dislike intermitant spark problems , then I will say it again . Thanks for any inputs you may have. Rick

Note: Every time I check the spark, it ALWAYS sparks those couple of revolutions after the starter button is released...same thing with the pull rope

 

Quickly check resistance on the pick up coil and stator when it's in one of those no start phases and see if either is out of acceptable range. Plus even a good blast with a heat gun on the stator and pick up area for a few minutes may reveal something.Plus even a tiny bare spot on an ignition coil wire that could short to ground could give people fits.

 

Yes, I have quikly disconnected stator and pulse coil after the engine died....several times and they check good. I traced the coil primary.....no damages to the wire.....all this is my delima. Hmmm...the heat gun? No, never tried that before...on anything. Are you thinking that the heat may cause the pulse coil or stator to show a failure during the resistance checks?

 

They're both coils and coils can weaken over a period of time from age,heat,etc. Just a thought.

 

^^^^^ I will try this. I googled the issue and others have found that placing heat on the CDI can help it to function...and prove that its bad ( have always frozen them...ha, ha, ha ). I will use some heat and try the CDI, the pulser and the stator. I will follow up with my results. And, maybe an "old dog" can learn new tricks ( me)...

 

Just jogged my memory about an old TRX200 that came into the shop years ago with no spark. Had an old tech that worked for us awhile that grabbed it to check it out. Pulled the cdi and dropped it flat on the concrete and hooked it right back up and the machine cranked up.. Kinda impressed me as he said he'd done that on several Hondas like that and if they fired up,he'd go ahead and order cdis as most wouldn't run long. He was right. Killed the Honda and it wouldn't start back up again. New cdi solved the problem. Seems like every old tech has some weird tricks up their sleeves and many of them work.

 

^^^^ I agree and thanks for the story. Experience, and doing something is the best teacher, not the books. On this Bayou, I:
- Checked the CDI connections again, no corrosion, re-connected
- Cleaned the battery terminals ( already cleaned the negative ground to the
engine )
- Intalled another new spark plug
- Damned thing ran for 30 minutes, and I thought...Hmmmm...the battery
cables, tho I know poor battery condition and dirty cables can cause alot
of issues, it may be fixed....Yes!!!!!
- Then it dies. So I tried your idea about the heat gun and heated the CDI (
which goes completely against my teachings as my degree is in eletronics
engineering....cold is always better for electronics ).....and it starts and
runs...
- So, I will do it all over again tomorro...well...Monday and try to repeat
the failure/resurrection....
Again, knowlegde comes from experience....and there is no better teacher.
I will follow up once more and I think this "old dog" may have learned a new trick.

 

Well, darndest dang thing I have ever seen. Twice now I let the ATV run until it died ( 10 to 15 minutes ), and would not start back up........
- I had the heat gun connected and in place and ready,
- After about 15 seconds after the engine died, turned on the heat ( directed at
CDI, at approx 1 foot of distance from the CDI,
- After applying the heat for 60 seconds, engine fired back up...on both
occasions, and kept running. On one of the restarts, I let it run for 45 minutes.
I'm going to do this one more time as three times is a charm, and CDIs are
not cheap. But at this point I'm fairly convinced that the problem is the CDI, and applying heat temporarily resolves the issue.
OPT, thanks for the idea! An old dog can be taught new tricks!

 

Some tricks work,some don't.. Hope the cdi is the problem..

 

I also hit cdi with screwdriver handle pretty hard an most of the time it will crank up or spark everytime you hit cdi...Unplug plug wire put tester in plug resistor an watch tester while hitting the cdi an see if sparks when hit