I keep killing CDI's - Honda RC51 Forum : RC51 Motorcycle Forums
 
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post #1 of 10 (permalink) Old 12-19-2019, 12:17 PM Thread Starter
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I keep killing CDI's

Hello friends!
I've been away for a while because I had sold my Beloved RC51 to help pay some bills. Well, I just acquired another one! Yippee! But this one has a problem. When I got it she hadn't been started in about 5 years and I got her for a song. Now I know why. She had no spark so I assumed the CDI was bad. My Brother had a couple of spares that he gave me to try out. I plugged the new CDI in and Voila! She started. (Of course I had replaced the old gas, oil, brake fluid, etc.). I immediately put a multi-meter on the battery terminals and was getting about 14.5v DC at the battery. I'm a little sketchy on how to test the other components that could cause the CDI to burn up so any insight on that would be awesome because after 2 miles and back to my driveway the bike stalled. I checked the spark again and had nothing... again! So I assumed I burned up a second CDI. I was able to resurrect the first CDI by getting the 2 pairs of Transistors and replacing them per the instructions I found online. She starts again but I don't really want to run her for long until I test the other likely components.
Could it still be the Stator even if it seemed to be charging correctly?
How do I test the rectifier? Preferably without running the bike?
Is there something else I should be looking at as well?
Thanks in advance!
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post #2 of 10 (permalink) Old 12-19-2019, 12:42 PM
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with the engine revving at 4 or 5000 do you still have 14-14.5 volts? or are you much higher than that? if your system is going very high then it could cause issues, but it doesn't seem overly likely.


if your voltage is normal then chances are it's a low impedance circuit on the CDI output.

check for the condition of the wiring at the low side of the coils, check the coil packs themselves as well.


if you're burning out the transistors i'd suggest it's likely due to excessive current going through them due to low impedance on the output.
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post #3 of 10 (permalink) Old 12-19-2019, 01:14 PM Thread Starter
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Originally Posted by Wibbly View Post
with the engine revving at 4 or 5000 do you still have 14-14.5 volts? or are you much higher than that? if your system is going very high then it could cause issues, but it doesn't seem overly likely.


if your voltage is normal then chances are it's a low impedance circuit on the CDI output.

check for the condition of the wiring at the low side of the coils, check the coil packs themselves as well.


if you're burning out the transistors i'd suggest it's likely due to excessive current going through them due to low impedance on the output.
It hangs around the same as you rev the engine. I was planning to change out the coils next. I did notice that when I was checking for spark by resting the spark plug against a ground while turning the engine over that it shocked the crap out of me, even though I was holding the rubber boot. Is that normal? I'm not very electronically savvy but I seem to remember checking for spark that way on other vehicles and not getting shocked when I was holding the boot.
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post #4 of 10 (permalink) Old 12-19-2019, 02:19 PM
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if you're holding the boot you shouldn't get lit up, no.


now would be a good time to do the 600rr COP mod. its easy enough to do.
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post #5 of 10 (permalink) Old 12-19-2019, 02:56 PM Thread Starter
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Originally Posted by Wibbly View Post
if you're holding the boot you shouldn't get lit up, no.


now would be a good time to do the 600rr COP mod. its easy enough to do.
I just read up on that mod. Sounds like a good mod but I think I'm going to just get the stock coils first and see if that cures the problem without the potential of me screwing something up and now having 2 problems. Like I said, I'm not very electronically savvy. Mechanically, I'm good. Electronically, not so much.

Does it sound like it's there's a chance the coils, or at least the front one I was checking spark on, could be the culprit for my killing CDI's?
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post #6 of 10 (permalink) Old 12-19-2019, 02:59 PM
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if you have a ground fault on the high side of the coil it shouldn't bother the CDI. it's supposed to discharge to ground.

however if you have a circuit problem on the low side then the current output of the CDI will be elevated and could damage the transistors.

i'd strongly suggest inspecting the wire harness as it's associated with the ignition coils (yellow/blue and blue/yellow wires) and make sure that's all kosher.

if you have failing insulation within the coil then it could reduce circuit impedance. so check the cases for cracks or mechanical damage, chances are checking them with a multimeter won't get you anywhere as the actual resistance there is going to be low anyway.


but yeah, i'd replace the coils before i replaced another CDI



this is of course under the supposition that you don't have spark because of the CDI, and not because you've lost it due to cam or crank position signal loss.
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post #7 of 10 (permalink) Old 12-19-2019, 04:26 PM Thread Starter
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Originally Posted by Wibbly View Post
if you have a ground fault on the high side of the coil it shouldn't bother the CDI. it's supposed to discharge to ground.

however if you have a circuit problem on the low side then the current output of the CDI will be elevated and could damage the transistors.

i'd strongly suggest inspecting the wire harness as it's associated with the ignition coils (yellow/blue and blue/yellow wires) and make sure that's all kosher.

if you have failing insulation within the coil then it could reduce circuit impedance. so check the cases for cracks or mechanical damage, chances are checking them with a multimeter won't get you anywhere as the actual resistance there is going to be low anyway.


but yeah, i'd replace the coils before i replaced another CDI



this is of course under the supposition that you don't have spark because of the CDI, and not because you've lost it due to cam or crank position signal loss.
I'm pretty confident it was the CDI the second time because I did the "re-solder new Transistors" repair on the first one I killed and plugged it in and the bike started. I will check those wires though.
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post #8 of 10 (permalink) Old 12-20-2019, 10:39 AM Thread Starter
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Well... the Coil replacements will have to wait until the first of the year. I'll post once I've done it and hopefully my new Girl will be GTG!
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post #9 of 10 (permalink) Old 12-25-2019, 08:11 PM
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I had the same problem years back the burning out the CDI's. Checked coils leads etc, everything checked out fine. In the end I changed the wiring loom as well as the regulator rectifier with a Mosfet regulator rectifier.
Haven't had a problem since.
So yeah it worked for me...
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post #10 of 10 (permalink) Old 12-25-2019, 09:19 PM Thread Starter
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I had the same problem years back the burning out the CDI's. Checked coils leads etc, everything checked out fine. In the end I changed the wiring loom as well as the regulator rectifier with a Mosfet regulator rectifier.
Haven't had a problem since.
So yeah it worked for me...
Did you replace the whole harness or just the rear sub-harness? Or a different sub-harness?
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