CDI loose connection advice

[Bigtex]

Hey y’all pretty new to the forum so go easy on me! I’ve got an ‘85 big red in nice shape. I recently purchased it. It had this thing where it would randomly die. I replaced a few parts here and there, but realized the issue was caused by a loose connection on the cdi. I opened it up and cleaned the connectors and greased them but they were already in pristine condition. The problem persists. It’s not a big deal. If it dies or doesn’t start I just have to wiggle the connector. My question is how I should go about fixing it? I’m not sure if I should buy a new cdi or try and tape the old one real tight or what? Would a new cdi even help? I was thinking about a Hotshot. The connector seems to be perfectly fine by the way. Both sides are fully intact With the little latches still working and totally clean. Advise?

[ironchop]

Hey y’all pretty new to the forum so go easy on me! I’ve got an ‘85 big red in nice shape. I recently purchased it. It had this thing where it would randomly die. I replaced a few parts here and there, but realized the issue was caused by a loose connection on the cdi. I opened it up and cleaned the connectors and greased them but they were already in pristine condition. The problem persists. It’s not a big deal. If it dies or doesn’t start I just have to wiggle the connector. My question is how I should go about fixing it? I’m not sure if I should buy a new cdi or try and tape the old one real tight or what? Would a new cdi even help? I was thinking about a Hotshot. The connector seems to be perfectly fine by the way. Both sides are fully intact With the little latches still working and totally clean. Advise?I've been told by a couple different Honda guys that the CDI itself doesn't wear out but that the reason they stop working is usually due to a soldered connection inside the box coming loose from the plug connector.

If it starts when you wiggle the plug, I'm guessing that what I heard might be your problem. Loose solder connection inside the CDI box itself and not so much the plug-in socket on the outside.

As far as a fix for that particular problem, I'm not aware of any outside of replacing the whole unit, but I'm no expert on the matter. Hopefully someone else can give you that answer.





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[Bigtex]

That’s interesting. It very well could be the issue. I found a $10 Chinese replacement so I’m gonna order that and see if it makes a difference. I figure $10 won’t hurt anything. Thanks for the advice! Any other help is greatly appreciated.

[350for350]

If nothing else, Ps2fixer makes a plug that your use to put the later 250ES style CDI's on your 85. Just cut your wires off, solder his in place and you're set to use the later CDI. The 85 CDIs were a one year only model, The 86-7 CDIs are more readily available and cheaper.

[ps2fixer]

I've been told by a couple different Honda guys that the CDI itself doesn't wear out but that the reason they stop working is usually due to a soldered connection inside the box coming loose from the plug connector.

If it starts when you wiggle the plug, I'm guessing that what I heard might be your problem. Loose solder connection inside the CDI box itself and not so much the plug-in socket on the outside.

As far as a fix for that particular problem, I'm not aware of any outside of replacing the whole unit, but I'm no expert on the matter. Hopefully someone else can give you that answer.

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I'd say that's 90% true, most common issue would be the solder joints internally like you said. The circuit has capacitors and over time they can loose their capacity like a battery does. Resisters also change resistance over time. A new proper CDI will have better spark than a 30 year old one, but not all CDI's are equal. From my experience the Chinese ones aren't a great solution, it might make the machine run but I have yet to have one run "right". My testing was done mainly with my 350x, so maybe it's more picky on the ignition. The way these CDI's work it's a bit of a balancing game between charging up the capacitor to a high voltage vs the capacity of the capacitor (think big batteries take longer to charge). Too small of a capacitor gets the high voltage, but doesn't have the energy storage to make a nice thick spark, while too big of a capacitor makes too low of a voltage and it won't jump as far, but should be a thick spark due to the higher amps.




As far as fixing the problem, you've stated the actual terminals and connectors are in great shape, so as long as the female terminal isn't loose fitting on the male terminals of the CDI, it should be the solder joints being bad. Since the CDI is effectively junk, you could try to cut the CDI plastic housing with a small cutting tool directly behind the connector and dig out the epoxy carefully (heat helps soften it, it's a challenge though). Once you get down to the circuit board, it's either reflow the solder to fix the broken joint, or if the pad on the circuit board is pulled up, you might have to make an actual circuit board level repair (effectively run a wire to a good part of the board). Once it's fixed and tested, you can refill the hole with epoxy, and if you did a clean cut, ideally you could push the plastic part back over to hole to try to make it look somewhat normal.

For throwing money at the problem, there's a couple people that sell aftermarket CDI's, from what I've heard, Mike's 250es CDI works well on the big reds, but you'll either need to update to the 86-87 style plug, or see if Mike still has the 85 -> 86-87 adapter (I make the adapters) I also make the pig tail to change the CDI connector if you don't mind the splice work. It's not hard but it's critical to seal the wires up for longevity. The 3M butt crimp connectors work well that has the adhesive heat shrink on it (typically pink, blue, or yellow).

There's always the option to just buy another used CDI, 85 250es and 250sx used the same CDI. You'll get a 30+ year old CDI, but for the most part they hold up quite well.


Since you've already gave China $10 for a CDI, if it does run on it, make sure it revs out GOOD, like the OEM one. If not the ignition timing built into the CDI might not be right. Another thing that would be a good thing to check is the max spark gap OEM vs Chinese. Standard min spec is a 6mm gap, and there's tools to measure it. Bigger the gap it can handle, the better quality your spark is, the 6mm spec is just the bare min to say the ignition system is ok.


I've been wanting to make my own CDI, even just for personal use, but I haven't been able to focus on that project much. If you get a solution figured out with your machine and are looking to throw the OEM CDI in the trash, I'll pay the shipping to get it so I can take it apart and see how the OEM design is. Maybe if things work out I'll reproduce the OEM CDI design, but I'd like to give the digital CDI concept a shot too since they have more control and such (easy start being a nice feature that can be added).