Electrical woes - opinions? - Honda RC51 Forum : RC51 Motorcycle Forums
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post #1 of 6 (permalink) Old 06-18-2017, 03:00 AM Thread Starter
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Electrical woes - opinions?

Hello fellow RVT,ers? I did search first, actually that helped me troubleshoot.

Got myself a bit of a challenge. I've been slowly working on the bike getting her back into great condition since I acquired her. As I said in my intro she's cosmetically rough. As I got in working out kinks (fuses, gauge replacements, turn signal relay, etc.) Anyway, got her out the other night and just got to the first stop in my neighborhood and she died and hasn't ran since. After testing and re-testing I replaced the battery. That didn't work so I replaced the plugs thinking I fouled them out (the old ones still look fine, only tried to crank her a few times.) I'm not getting any FI codes but the gauges load up fine however I have no spark.

Downloaded the factory service manual and started deeper troubleshooting. After thoroughly examining the harnesses and connectors the trouble really began. She was a mess, simple splices,cheap wires, and melted insulation in places. Then I get to the rectifier connectors and find it was burnt at (only visible after disconnecting it.) Further inspection found that the yellow wires on the rectifier were exposed near the base and likely shorted out. That was the first issue. Further testing revealed that the Engine pulse generator has no voltage 0.00 instead of .07 so at this point I am leaning there. My dilemma is that I'm not getting an FI code at all and since the gauges are showing good I'm worried it may be the CDI. Nothing is getting to the coils.

Now, the stand sensor is removed (can't find a bypass.) The position/lean sensor is fine (tested, it does cut the fuel.) The handle switch activates the primer which works (fuel smell is there.) I've bypassed a manual kill switch (maybe custom.) All of my fuses are clean including both 30 amps. The gauges read the neutral gear so I don't think it's that but just to test but it doesn't matter if I hold the clutch.

For now I've crimped connectors on the rectifier but I suspect it's burnt out. Before I start buying replacement parts I wanted to get your take. Should I go ahead and get pulse generator? I think at this point I'm going to try to get an entire harness replacement as well. Thoughts?

Oh happy Father's Day to my fellow dads as well.
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post #2 of 6 (permalink) Old 06-18-2017, 03:03 AM Thread Starter
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Additionally I disconnected the primer to ensure I don't ruin the new plugs for spark testing.
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post #3 of 6 (permalink) Old 08-18-2017, 06:55 PM Thread Starter
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Alright, well I have my answer and I'm back up and riding.

More than likely the CDI was fried due to the cross wiring and grounding out of the rectifier. Thankfully the repair manual and good use of a digital multimeter worked. Here is all I did.

1.) Replaced the positive battery terminal
2.) Replaced all fuses
3.) Replaced the battery
4.) Replaced the coil packs (the rear one actually fell apart)
5.) Replaced the relay (in with the stator, the name escapes me at the moment)
6.) Replaced the voltage regulator/rectifier
7.) Replaced the rear wiring harness/loom
8.) Replaced the CDI box (the grey one which is likely the culprit as it was my next to last ditch)

Everything ended up testing fine with my ECU and both of the coil packs had proper resistance but I replaced them anyway. The previous owner warned me he didn't know electrical very well and it certainly showed in the rear harness once I got into it. There were patched solder joints taped up inside the loom with different wire gauges and burnt wire insulation throughout. Replacing it all was by far the best bet in the long run as now I know everything about the bike electrically which is pleasantly simple.

Now onto replacing the fans with pushers and wrapping the exhaust since she runs hot.
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post #4 of 6 (permalink) Old 08-20-2017, 06:49 PM
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Very good follow up. Thanks for bringing that. Pricey fix, but you know that system now and should be good for the rest of the time you have the bike.

John, 2000 RC51 #000100

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post #5 of 6 (permalink) Old 08-20-2017, 08:46 PM
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damn, i hate it when i get something thats a disaster because someone doesnt know what they are doing and ruins it. good job and make her whole again!

lovin' my little torque monster.
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post #6 of 6 (permalink) Old 08-22-2017, 08:44 AM
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I have a SP2 harness for sale if your interested, pm me.


2003 SP2: Everything I could find.
1991 Honda HawkGT
2008 XR650L
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