weak spark

[r-chri12]

1993 honda 300ex,what triggers the cdi box to create ign. spark,and where is it located? I have replaced the coil and plug and still have a weak spark,quad pops and cracks on accel seems like an ignition issue to me any will be appreciated RC

[brian 68]

i would first check for intake leaks, and make sure carb is clean and jetted right. then check the timing chain, and tensioner. btw you did gap your plugs right? does the quad idle ? hows the top end?

[brian 68]

sorry but to answer your question the pickup on the stator sends a signal to the cdi telling it when to fire the coil

[r-chri12]

I had already gapped the plug at factory spec and ckd for vac. leaks at intake I also adjusted valve cearance .004 in-.006 ex. I,ve adjusted the needle jet 1 notch at a time and this did,nt seem to make any difference in performance good or bad I just bought this for my son(13 year old) the only thing aftermarket that I can see is a Cobra exhaust system and a K-N air filter I think everything else is stock,Ive ordered a service manual but have,nt received it yet thats why I was wondering where the ign. pickup/trigger is located if it even has one I don,t know exactly how this cdi system works as I am not that familiar with the ign. system on this quad,I,ve been a auto tech for 37 years and just the way it runs and sounds it seems like an ign. problem and not a fuel issue ,thanks for your help and I,ll recheck your suggestions RC

[wilkin250r]

The ignition systems on these quads are really simple.

The stator has a few coils on it dedicated to the ignition system, called the exciter coils. They provide POWER for the spark, but not the timing. That gets fed to the CDI box, and charges up a capacitor to several hundred volts.

There is a pickup coil that sits outside the flywheel, and that's where your timing comes in. It senses a little bump on the outside of the flywheel, and sends a pulse to the CDI.

When the CDI box recieves that trigger pulse, it waits a small predetermined amount of time (based on RPM), and then dumps all that energy from the capacitor directly to the ignition coil, which bumps it from several hundred to several thousand volts.



I doubt your pulse trigger is the problem. A weak pulse won't result in a weak spark, it doesn't get amplified or anything, it's just for timing.

The exciter coils are really easy to check, because they are just a coil of wire. Not too much can go wrong, either the wire shorts out (which would show up in a simple resistance check), or the wire breaks and isn't a complete circuit (which would also show up in a resistance check). I don't have the spec, but a simple resistance check is all that is needed, it's a fairly reliable test.


Sounds to me like it might be your CDI, but I would check the other things first.

Anybody have the specs?

[r-chri12]

Thanks for your help if you ever need any advice concerning a Ford motor product drop me a line RC

[brian 68]

i didn't think it sounded like a ign problem , but if it is the cdi is what i would check. the reason i ask about idle, top end. if the timing chain is worn they will miss under acceleration, and sometimes when let off.
do you have a stock exhaust to try? if its leaking bad, or has the guts out of the can, it can cause a low to mid miss.