Chasing a gremlin

R

Rockenstein

New Member
I was out the other night cruising with no particular place to go and my little engine is ticking along like a Timex at all speeds...I slow up for an upcoming traffic light and as soon as it was at the speed where the centrifugal clutch disengages it stalled out. I peddled it into a nearby parking lot that was well lit and check all the usual things like fuel, plug wire etc and still it just won't go no matter how fast I peddle or how much I choke it so I head for home which of course is now 7km away! I get it home and pull the plug...it's sopping wet and looking really fouled so I put a fresh one in. When I go to put the plug boot on it self destructs, tried to reassemble it but the plastic threads inside it that hold the brass part are stripped but luckily I had another boot I could use. I get the plug wired back up, kick it over and it starts...I let it idle for say 30 seconds in my shop and then shut it down figuring it's good to go. Next day I take it out back to the parking lot and get ready to warm it up before I set out on a venture to do a few things...starts right up and idles but it felt funny in that it just did not want to take any throttle. Not taking throttle when it's cold is sort of normal for mine but normally after about a minute of warming up it's good to go but this time after about 2 minutes it's still not liking throttle input and at about 2 1/2 minutes it just quits again. I lug it back into the shop and pulled the plug...looks ok, it's not sopping wet and not really smelling of gas so I pull the carb, disassemble it, blow out the jet, clean the bowl, etc etc and then reassemble. Kick it over a dozen times and nothing...pulled the plug and checked for spark and good looking spark we have. I'm thinking ok maybe I chewed up a crank seal so I put the plug back in, blocked off the exhaust port with a makeshift plate and ground down a rim valve so it fits nicely in the intake tube. I pressurized the crankcase to about 10 psi and brushed a thick soap mix around the seals and crankcase gaskets...not a bubble is seen. By this time I'm really scratching my head as to what the heck is going on so I get out my DVM and check the ohms on the winds of my magneto and compare with the info posted on here and the magneto is looking to be ok. Again I pull the plug and check for spark and I have spark. I also pulled the magnet rotor off, wiped it down, and the magnetism feels like it's good enough to generate proper current in the magneto. So the point I'm at now is all that's left that could be wrong is the CDI but I'm skeptical of that thought because in my experience electrical components normally work or they don't work...and I do have spark outside the cylinder. Right now my engine will fire briefly but will not catch and then idle at all like it was when I took it out to warm it up. I'll add too that I've checked the line from my aftermarket kill switch for a potential grounding out...also did the same for the plug wire and the wires leading to the CDI.


Has anyone ever had a CDI fail slowly?


:-||
 
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I'm feeling secure now in saying that my CDI is failing\has failed...

I double checked all the possibles again earlier this afternoon and then went out and gave it a try...it popped a couple times but never fired up completely. I pulled the plug, grounded it with a length of copper wire secured to the engine, kicked it over and sure enough no spark. I let it sit for about 30 minutes then went back out and kicked it over again and this time there was spark. I left the plug out and pedaled it around the parking lot and for about 2 laps I had spark then nothing again. Since about an hour ago it's been sitting here in the shop, I just now went and kicked it over with the plug out and still grounded with the length of copper wire...it's got spark again. Ya know it's probably a cold solder joint or a 10 cent resistor inside the CDI that's causing all the grief, it's really too bad that they are encased in epoxy and rendered non serviceable. Right now I'm wishing that the Chinese had have went with the points ignition setup that the Russian bicycle engines used...service and diagnostics would certainly be more simplified.


Hope this info maybe helps others.


Cheers...
 
Rock,
After you replace the CDI let us know what happens. This is the second time I've seen the issue of intermittent ignition discussed here. I'm like you; I wish we could get more info on the CDI. A couple of guys have tried unsuccessfuly to dissect one of the little buggers but so far I haven't seen where anyone has found out exactly what's buried in that epoxy. Keep us informed and good luck.
Tom
 
Unfortionatly spark likes to break down under load. Could have seen it with a lab scope. The first CDI that was breaking down on me felt warm to the touch. If that helps anyone. Now when there is a next time if it comes I watch it on my Fluke Lab Scope!
 
That was part me remembering thinking out loud what I did I road that limping thing around awhile. I even strapped a unlit propane bottle to the back of the carb vi a hose to prove my fuel was right. Mine never really fowled a plug just ran with no power. Then later I remembered the Lab Scope . Doh! Oh the propane was on there as extra fuel in the case it was starvation. Don't wanna leave one of those on your not oiling right. Was Diagnostic purpose only!! That was when I touch the CDI and felt it was warm. Shorting out internally .
 
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Well a new one at Thatsdax is 8 bucks. Another guy in the other forum got a cdi off a yamaha 80 that was a 2 wire to work great. Kinda rare to have one of those laying around. GL
 
My CDI finally arrived yesterday morning and after I reassembled my MB and got out on the road the engine fired right up and ran as it was before with the fresh CDI plugged in. I'm baffled about why the original failed but hey...it's all part of the fun. My old CDI has been soaking in a half liter of gas since my last post in this thread. Soaking has softened up the epoxy a little but it's not even close to being soft enough to get a look at it's innards easily.

Cheers..
 
a soldering gun with high enough oomph will crumble the epoxy I did that with my cheap iron until it died(dropped it broke off the tip) had a bunch of electronic parts stuffed inside coil, condenser, and a circuit board with caps etc.
Not knowing much about electronics I didn't do any thing more to it
 
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