I keep killing CDI's - Page 2 - Honda RC51 Forum : RC51 Motorcycle Forums
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post #11 of 19 (permalink) Old 02-27-2020, 09:40 AM Thread Starter
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Well... I've done a lot of digging around and a lot of checking wires and replacing parts. I replaced the Stator because it would drop voltage down to 5 volts as the bike ran (with the Stator disconnected and running on the Battery). I swapped out the Regulator/Rectifier because I had a spare. The fuel pump was intermittent so I just ordered a replacement Fuel Pump. Should be here tomorrow. I replaced both coils just because. The only thing I wasn't able to find a replacement for was the Rear Wiring Harness where all of this other stuff connects. If anyone has one they are willing to part with I'd be happy to buy it. Since I'm not able to find enough information to make an informed conclusion I just threw everything at the problem but the kitchen sink.
I checked all of the ground wires to make sure they made it to the chassis ground. I checked voltage, resistance, continuity and everything else I could figure out.
Hopefully this weekend I can get the replacement fuel pump installed and get her back together enough to run her for a while. We'll see what happens. Bike-week is right around the corner!
Thank You to everyone who responded trying to help me. I truly appreciate it!
... Fingers crossed!
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post #12 of 19 (permalink) Old 03-01-2020, 07:35 PM Thread Starter
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I may have figured it out. In the beginning I said the bike had been sitting for 5 years. I think some of that time was spent outside in the weather. It seemed like there had to be multiple different problems. The main one was a grounding problem that was killing CDI box and causing the fuel pump to be intermittent. I traced the fuel pump ground problem to a "connector" that appeared to be a termination point for all of the green (ground) wires. It took some doing to get it apart but I got it. Seems to be a grounding block of some kind. All of the connectors had white powdery residue that is obviously causing bad connections. I'll be cleaning it up and putting the harness back together ASAP. I'll let you all know how it goes. Again... fingers crossed!
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post #13 of 19 (permalink) Old 03-01-2020, 08:22 PM
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Originally Posted by oneshot onekill View Post
I may have figured it out. In the beginning I said the bike had been sitting for 5 years. I think some of that time was spent outside in the weather. It seemed like there had to be multiple different problems. The main one was a grounding problem that was killing CDI box and causing the fuel pump to be intermittent. I traced the fuel pump ground problem to a "connector" that appeared to be a termination point for all of the green (ground) wires. It took some doing to get it apart but I got it. Seems to be a grounding block of some kind. All of the connectors had white powdery residue that is obviously causing bad connections. I'll be cleaning it up and putting the harness back together ASAP. I'll let you all know how it goes. Again... fingers crossed!
That's corrosion , coat any connections you can get to with dielectric grease. They sell it at auto parts stores in a tube like toothpaste.
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post #14 of 19 (permalink) Old 03-02-2020, 01:49 AM
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the ground block can cause all kinds of issues, but unfortunately for you it has nothing to do with the CDI. the grounding point for the coils is actually on the other side of the bike (under the rider's seat on the right side)
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post #15 of 19 (permalink) Old 03-02-2020, 06:50 AM Thread Starter
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the ground block can cause all kinds of issues, but unfortunately for you it has nothing to do with the CDI. the grounding point for the coils is actually on the other side of the bike (under the rider's seat on the right side)
Well it definitely has to do with the fuel pump. I think it might be a player in ALL grounding because it seems to terminate at that main ground on the right side, under the seat. At least some of the grounds from it go there eventually because I checked that.
I replaced both coils earlier in my attempts to fix this... and checked their grounds.
I just wish there was a way to check the input to the CDI or whatever else I'd need to check on the actual CDI.
Even if this does seem to fix everything I'll still be hard pressed to take any long rides, at least until my confidence is restored.

Last edited by oneshot onekill; 03-02-2020 at 10:05 AM.
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post #16 of 19 (permalink) Old 03-02-2020, 12:10 PM
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that ground block handles all kinds of things, and the fuel pump is probably included there. clean the everliving shit out of it and seal it up with dielectric grease, then waterproof it. your bike will love you for it.


you can check the signals in and out of the CDI, but to do a good job of it you'll want a scope. if you have a high quality meter you can measure max voltage out, or buy a shitty peak voltage adapter if you don't have a good meter.

the signal between the ECU and the CDI isn't something that will wreck a cdi, those are just gate pulses to the transistors on board. you'd want to use a scope to check these.
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post #17 of 19 (permalink) Old 03-02-2020, 03:48 PM Thread Starter
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that ground block handles all kinds of things, and the fuel pump is probably included there. clean the everliving shit out of it and seal it up with dielectric grease, then waterproof it. your bike will love you for it.


you can check the signals in and out of the CDI, but to do a good job of it you'll want a scope. if you have a high quality meter you can measure max voltage out, or buy a shitty peak voltage adapter if you don't have a good meter.

the signal between the ECU and the CDI isn't something that will wreck a cdi, those are just gate pulses to the transistors on board. you'd want to use a scope to check these.
Well, I don't think I'm electronically savvy enough to do a proper test. I think if it runs for me I'll just ride it around my block as many times as I can without pissing off the neighborhood too much. Then do it again the next day and the next and the next, until I'm confident in my repair work. Wish me luck!
Thanks again for all of the help!
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post #18 of 19 (permalink) Old 03-04-2020, 10:59 AM Thread Starter
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Last night I re-wrapped the rear wiring harness after discovering the Ground Block was full of oxidation, cleaning it and re-assembling it. Then I put the harness back in the Bike. By the time I was finished it was too late to start it. But I did turn the key on to make sure everything looked and sounded right. The lights all came on, the fuel pump spooled up nicely. Now I just need to run it. My time is tight for the rest of this week so it might be the weekend before I get the chance.
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post #19 of 19 (permalink) Old Today, 10:51 AM Thread Starter
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This past weekend I was able to start my Baby. I rolled her out of the Garage and into the driveway, gave her a little pat on the top of the tank and pushed the start button. She fired up immediately without even using the fast-idle knob. I immediately put the Multi-meter on the battery and discovered that the voltage was right at 15 volts and was slowly climbing so I shut her down. I disconnected the Stator and tested the yellow leads with the motor running but the stator disconnected. It was 30 volts AC at idle (which my idle is a little high at 1600 RPM's) and climbed up around 90 volts at 5000 RPM's. That seemed a little high but I read that as long as it's consistent across all 3 leads and isn't crazy high that's OK. So I replaced the Rectifier/regulator with an extra that I had and tried again. Started right up again but this time the voltage at the Battery was around 14.5 volts DC and stayed there as I rolled the throttle to around 5000 RPM's. I let her run for about 30 Minutes in the driveway and watched the Multi-meter as the fans kicked on and off. When the fans came on it dropped to around 13.5 volts because of the draw but only for a second and then went back up to around 14.5 volts. I put the fairings back on and fired her up again (hoping I didn't mess something up putting the fairings back on). She fired right up so I took her for a ride around the block. AWESOME! Everything went great so I did another round, and another, and another. Next ride... maybe tonight... I might venture to the gas station to put some non-ethanol gas in her.
I'm really hopeful that she's finally fixed and thankful to everyone here who helped me to understand what might or might not be happening!
I'll post again after more rides...

As far as what actually fixed the problem, I think it was a combination of problems that became compounded because the Bike sat for 5 years and some of those were probably spent outside. To recap, the parts I replaced were: Stator, Rectifier/Regulator, coils, CDI (Repaired) and fuel pump.

Last edited by oneshot onekill; Today at 01:28 PM.
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