What kills CDI'S

Apr 22, 2003
When i was last time back home a friend of mine who used to work in a place that repaired CDI boxes told me the main reason why they die is because the charging system cooks them and what to do to prevent this from happening.
Now i hope i can get the explanation right here but the example he gave me was for my Suzuki GSXR 1100 and even though some bikes have a different system the same princaples apply.
On the suzuki it has an external alternator with a built in regulator which has 2 wires leaving it, the wire that carries the current back to the regulator has to through plugs and switches and so on, so if you have any dirty connections in this circuit you get resistance, so by the time it gets back to the regulator you have a voltage drop, the regulator sences this and thinks the battery heeds to be charged and keeps putting volts down the line to charge the battery, In turn the CDI is getting constantly hammered with over voltage and fries.
Cut the wire coming back to the regulator and install a head light relay, use the wire coming back through all those plugs and switches to activate the relay and then run a wire from the regulator through the relay direct to the battery, by doing this you eliminate any chance of the regulator getting the wrong signal and you dont fry your CDI.
Im no wizard with electronics so i hope you can understand my explanation, if not i can show you a sketch he gave me on how to do this and it may be a bit clearer to you then
Oct 17, 2006
A great tip and a great solution to a potentially expesive problem as CDI unit can cost the earth.

Sep 30, 2006
Once upon a time a long time ago
My BM died completely as I pulled up at road junction on Loch Lomand Scotland, I was 2 hours into a tour heading towards the Pyrenees in Spain.
This is a bike that never gives problems so I was a bit dismayed to say the least.
The Scottish open golf championship was on at the time and there was a heavy police presence. The whole place was booked up because of the golf so there I was stuck in a car park early evening and running out of options.
The engine was completely dead; the engine would spin on the starter but would not run - weird - remember the BM has fuel injection and is run by a box of tricks.
A local biker came out to help and we scratched our heads in disbelief for an hour and a half, we tried everything we could think of to figure out what was going on.
eventually I said to him lets have one more go as by this time the battery was almost dead, and then the bike just started up at a touch of the button and sat on tick over as though nothing had ever happened.
it really was the weirdest thing
The rest of the trip which was some 3000 miles I had absolutely no problems with the bike, never had any problems before that occasion and never had any since
That autumn I was at the bike show at the NEC in Birmingham and relayed the story to the chief BMW engineer on their stand, he concluded that the only thing he could think of which could knock out the bike in the manner I had explained was a very strong radio signal which would knock out the CDI and as the police were very active policing the open golf championship and I remembered passing a police car just as the bike went dead he reckoned that was what did it.......I had been zapped by a strong radio signal from the police car which had knocked out my CDI.


Nov 5, 2003

Regrettably I'm old enough to remember the first production car in the UK with electronic fuel injection. The Renault 16 year ????. Until they recalled them and installed some RFI sheilding the M1 near Rugby, was a R16 graveyard. BBC? has a hi powered shortwave radio bradcast station there. It's still there.
Oct 17, 2006
A lot of new 2005, 2006 model cars immobilisers are being knocked out in the UK by police radio transmitters.