Fried CDIs - Honda RC51 Forum : RC51 Motorcycle Forums
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post #1 of 5 (permalink) Old 04-27-2017, 05:29 PM Thread Starter
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Fried CDIs

Hi to all,

I hope you will be able to help me with this

So CDI keeps failing on my '05 RVT and I can't seem to find what's causing it
Here's the story.
Bike was stored away for winter in a garage - petrol tank full, battery took out and on minder in my apartment. Bike itself was in one of those huge zip-lock bags to keep dampness away.
One weekend, when good weather finally came I took it out and did oil service and clean.
During it a rain cloud appear seemingly from nowhere (usual Irish weather) and downpour for approx 5 minutes before bike got covered. The service was finished, side panels put back on and next day went out for a spin.
After some 70kms engine died - due to, what was discovered later, fried CDI.
On the side of the road, I checked for usual, dodgy killswitch, burned fuses, broken wires around battery (due to vibration once gear indicator wire snapped on and clocks stopped working). I've noticed that there was moisture in the ECU plugs.
As I had trackday booked I had to get bike sorted within few days so got 2nd hand CDI off ebay with express delivery. Mechanic checked the loom for visible damage, and once CDI replacement was delivered, checked the charging system - bang-on 14.5 V gear independent.
Bike spent about half hour on dyno and another bit idling - there was no issue. So I collected it and drove back home (~50kms) and CDI failed again - fortunately not too far to push it home.

Relevant mods on bike:
PC3
Soft rev limiter eliminator
HealThech speedohealer and gear indicator
aftermarket Reg/Rectifier (bigger with heat sinking fins - I don't know the make)

Now, as the charging system seemed to be alright I'm going to check and replace spark plugs and leads (maybe will do 600rr mod while there), check earth on the engine block for corrosion and all the plugs and cables I can see while fairings are off.
CDI will hopefully be fixed with replaced thyristors - upgrading all 4 of them to 13A rated ones (stock are 5 and 3 as I recall).
Assuming the I won't find anything obvious, what else could be casing CDI to fail?
Could the ECU be damaged as a result of rain? Is there any way to test it (other than swap)?
What are other reasons for CDI failure other than RR/bad battery?
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post #2 of 5 (permalink) Old 04-27-2017, 11:40 PM
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i would expect low impedance on one of the outputs.

the ecu drives the gates in the cdi, and the actual power to the coils comes from the 30 amp fuse by the battery. if you have a low impedance circuit on one of your coils it could burn up the thyristors, especially at high rpm.


now would be a good time to do a coil over plug setup.
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post #3 of 5 (permalink) Old 04-28-2017, 02:08 AM
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(usual Irish weather) is the bike a US import? shouldn't need the soft rev limiter mod otherwise
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post #4 of 5 (permalink) Old 05-03-2017, 06:05 PM Thread Starter
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I have posted here yesterday but for some reason the post is not approved by mod yet - I guess it's because I attached photos to it...?

So in hope that kind moderator will approve the post and it will appear here I'll keep it brief

I got CDI repaired with new thyrsistors.
Tried to start bike and I heard a pop that sounded like an ignition on one cylinder - battery was week so only gave few cranks.
Change spark plugs and discovered lower cylinder one was badly corroded (here pictures were handy).
Next day with fresh plugs and fully charged battery bike didn't start.
I kinda hope that i blew CDI trying to start the bike with bad plugs and weak battery, so going to get CDI done again and give it another go.

Now I'm seriously thinking of 600rr mod to get rid off those bulky coils and leads.

@dansp1 , yes, it 's US import!
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post #5 of 5 (permalink) Old 05-04-2017, 10:17 AM
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need to get your post count up to post pics
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