Originally Posted by Tim McKittrick
I think I may have mentioned before I had a similar failure with my RS250- no load spark test produced a fat loud spark and it looked like everything was happy, but the bike ran poorly if at all. The affected cylinder would have a wet plug and it looked a ll the world like a fueling issue.
I end up replacing the coils as the connector to them was a fussy proprietary HRC bit and was a bit damaged- the solution was to replace the coils and the entire harness.
It would seem more likely that a coil would produce intermittent results than a CDI box- in my experience the CDI components are almost binary in use, either they work or they don't. If you haven't already swapped out the coil it might be an easy and cheap(ish) thing to try.
At this point we are all amazed you have had the nerve to stick with this as long as you have- and I think we all want to encourage you to not throw in the towel.
Also we all want to know the answer.
I'm with you, it'd be nice to find out what's going wrong. I'll take a running bike, but if it spontaneously combusts and a little brass plate with what was wrong with the bike engraved on it flies out in the ensuing explosion, i'd be ok with that.
I hope it's a hilariously easy problem that clears it right up, that's the ending this thread needs. "Whoops, plug wire wasn't in all the way!"
Edit: Forgot to actually respond to questions:
Don't know if the crankcase compression is ok, it sucks through the reed cage, doesnt come back out, squirts into the chamber at idle, working enough for me. As i understand it (and in my experience) leaky crankcases are the worst at idle. I could actually run my old ct3 with one reed missing if i revved it enough, hah.
Inductive ignition is just points right? Never heard it called that, new words, yay! I do wonder if i'll have to swap the coil over as well. Would make sense as its just a source coil voltage being broken instead of the cdi shooting a bajillion volts into it. Then again i can fire this coil by poking it with a 6v battery charger so i dont think that's as important.
Actually made my own wiring harness this last week and completely bypassed the bikes harness, didn't change how it behaved at all. Still trouble revving, very flat at high RPM, bizzaro spark test.
I don't feel too bad for saying i'm not going to put my CDI in my oven as an attempt to permanently fix my problems with it, lol. That's pretty wacky though, someone needs to tell yamaha that heating a component will fix it instead of inducing a heat related failure as is suggested in almost every service manual i have ever read
I could see a capacitor failing due to age (they kind of just do that, they puff up and stop being capacitors), i dont see how a thyristor could fail, or how a resistor could fail. I could see how a source coil or pulser coil could fail but the failure mode would be backwards in this case. It should get worse with heat, not better, and in my experience they fail in a binary way. Either working, or not working.
This saga has taught me a few things, though. Had an xl250s with a cracked coil at work that looked at first blush like water intrusion failed the ignition coil and that's why it wasn't sparking. Hit it with 12 volts dragging the leads across the ground, got spark. Checked the pulser coil, bam, no voltage. Replaced the pulser, suddenly we're sparking again and leaking voltage out of every crack and pinhole in the ignition system
I wish i had a fixing buddy with this bike to confirm i'm not retarded, or going crazy, and it is actually this hard to get it working correctly. No worries about giving up so far, i can't let it whoop me. I'll have it running hell or high water (seems like today high water isn't going to be a problem ><). I don't know if anyone saw my thread on the VW with the subaru motor that was acting funny and had me going for a month until i realized i built the harness slightly incorrectly and had the cranking imput voltage for the computer connected to key on voltage, tricking the computer into thinking it was still trying to crank over and obviously not starting, leading to it retarding the timing in two degree steps until the idle circuit took over and jacked the RPM back up. Uhg.
So as a question, what should the spark test look like for this? I kick it over and it's practically a daft punk show of sparks? Or is it more like one or two sparks per kick and that's it?