2nd bad magnedo and cdi in a week

joey d

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Joined
Dec 23, 2009
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Location
menlo park, ca
last week I went on a ride and my bike died peddled it home discovered I had no continuity between the black and the blue wire on both the cdi and the magneto so I believe the magneto went and fried the cdi in the process. all wires were soldered shrink rapped and taped no moisture in the magneto because it was sealed properly.
blue to blue
black to black
kill between blue and black

figured the thin wire on the magneto coil broke from excessive vibration. I was at wot and moving.

I replaced the cdi and the magneto. ran great again. put on a expansion chamber exhaust and an auto chain tensioner. took it on a 20mile ride. It ran great.
3 days later I take it for another ride and it ran like **** bogging stuttering and dieing at stop signs. Then it died completely.

I peddled my bike home again and now I have no continuity between the black and blue on the cdi and the magneto again. what is going on I never had this problem before with any of my other builds. I also never had a build that went this fast before When running right I'm getting up to 38mph. but I keep killing the electronics.
any suggestions would be appreciated.
 
Maybe your kill switch is shorting out intermittently?

I don't know what the cdi unit should measure (if you can even measure it), the magneto coil should measure something, probably in the range of 10s to 100s of ohms (the exact value should be on here somewhere).

I find it hard to believe that you killed 2 cdi's & 2 coils in such a short period of time, something else must be going on...
 
I have tried disconnecting the kill switch. just took a better look at the first magneto. It had a brake where the thin wire coming off the coil is soldered to the metal bar (aka ground). I resoldered the connection and now am getting some readings. These measurements have been done on a work bench.

magneto
blue to white=342 ohms
white to metal plate(black)=2.5 ohms
blue to metal plate(black)=345ohms

coil
screw and blue open
screw and black 6.82k ohms
blue and black 244.5k ohms

I haven't gotten to see if the other magneto has the same problem. I have to check if the little coil wire soldered to the plate is broken but That is what I suspect. being the same symptoms with the open black.

My question has this been a problem for anyone else out there. If you have a bad magneto laying around that just quit (not due to water damage) please look at this wire going to the plate and tell me if it is broken.

thanks joey d
 
Your kill switch should not be between the blue and black wires. That will fry magneto coils.
The kill switch should be between the black and white wires. This is a higher impedance, more loosely coupled coil that can handle a short. The blue/black coil can't.
If you really don't want to use the white wire, for some reason, use a normally closed PB switch on the blue wire for a kill switch, to open the circuit. (It's a bit harder to find a suitable normally closed switch, though.)

... Steve
 
Your kill switch should not be between the blue and black wires. That will fry magneto coils.
The kill switch should be between the black and white wires. This is a higher impedance, more loosely coupled coil that can handle a short. The blue/black coil can't.
If you really don't want to use the white wire, for some reason, use a normally closed PB switch on the blue wire for a kill switch, to open the circuit. (It's a bit harder to find a suitable normally closed switch, though.)

... Steve

Steve I'm with you. Either between the black (ground) and white (hot), or one wire from kill switch to ground on bike (assuming the engine is not insulated) and the other to the white wire. On ALL instillations I remove the stock wires and solder new wires (16 or 18G) that will reach my CDI.
 
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why does everything I have read keep saying to just cap off the white wire? This is very confusing. Also I have hooked up my friends bike the same way. He rides his 35milles to work and back every day no problems. mine I haven't been able to make it 3 rides without having the magneto coil lose continuity between the blue and ground.

I am beginning it is vibration related because there is no burning smell just a broken wire.
 
why does everything I have read keep saying to just cap off the white wire?

Because you're reading the wrong posts. There is a lot of misinformation on this site, on many issues.
There are also many posts saying to use the white wire for lighting.
The white wire was intended for the purpose of connecting a kill switch. Some people think that they know more than the designer. They don't. Just stick to the recommended wiring and you shouldn't have any problems.
This subject comes up every week or two.

... Steve

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thanks I better rewire my friends before his brakes too. thing is he has been riding his 30miles each way to and from work for about a month now no electrical problems wired kill between blue and black. mine lasts a couple days.
 
Right out of the book.



I run both wires to the CDI and connect one to the WHITE (Hot) and the other to the BLACK (Ground). I also have hooked the kill switch wires to the Blue and Black wires on the CDI without issues. I don't like tucking one wire under the handle and prefer a good solid ground connection. Like I said before I redo all the wires (16 or 18ga) from the engine, that way I have connections at the CDI and if a problem shows up I have isolated where the problem can be.
 

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thanks

I took a look at the 2nd magneto and It was the same problem. The thin coil wire was broken between where it comes through the plastic and the solider. I put some more solider on them both so now I have a spare. As for the cdi I was wrong about blowing them They both seem to be working. I am going to hook up my kill to the white and ground/black and hopefully I wont have this problem again. I still think it could have been vibration so I am gonna put a drop of epoxy on the wire too for reinforcement.
 
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