My junky CDI went out

placidscene · Oct 11, 2012

Anyone know where to get a decent CDI without building your own and without paying $75 for the Jaguar?
I don't want to replace my crappy china one that broke so quickly with another of the same type.
I have done searches thought the forum to find something else and keep coming up without a good answer to this problem. One person said they are using the Puch CDI, but they didn't say if it was working out ok.

JonnyR · Oct 11, 2012

why not just get another china CDI they arnt usualy that bad

maurtis · Oct 12, 2012

I still have my old stock CDI, it just needs a new plug wire. You can have it for free. I live in Kyle but go to the office in Austin on Mondays so can meet up with you.

If interested, I can throw in my blown motor with centrifugal clutch too! If you can get the clutch off (it did not come with a puller), it should still be in pretty good shape...

bigbutterbean · Oct 18, 2012

Not to hijack anyone's thread or anything, but since we're on the subject, should cdi's be replaced every so often? I know this may sound like an odd question, so let me explain. Certain parts need replacing after so many miles or whatever due to wear and tear. Is the cdi one of them? Mine is two years old, should I replace it, or as long as its working its fine?

placidscene · Nov 26, 2012

Well I finally broke down and just bought another $10 china CDI.
I will be putting it on next week after I get back from out of state and am very much looking forward to riding again!

2door · Nov 26, 2012

Five years into this hobby, seven bikes built and I've lost track of milage. Never replaced or had to replace a CDI, yet. And would certainly NEVER spend $75.00 for one.

Tom

Mopig · Dec 4, 2012

Problem resolved.

biknut · Dec 5, 2012

placidscene said:
Anyone know where to get a decent CDI without building your own and without paying $75 for the Jaguar?
I don't want to replace my crappy china one that broke so quickly with another of the same type.
I have done searches thought the forum to find something else and keep coming up without a good answer to this problem. One person said they are using the Puch CDI, but they didn't say if it was working out ok.

I've had a few fail too. This is my theory why they fail, and how to stop it.

It's a combination of heat, and the stock kill switch. We both live in Texas where it's HOT. The stock kill switch shorts the magneto windings, to stop the motor. Shorting the windings is not a good thing for the winding. Magneto coil windings run warm under normal operation. In hot weather, it's possible the extra abuse of shorting the winds may burn them up, causing the coil to go open.

Buy a kill switch from SBP. Their switch will allow you to wire it differently so you won't need to short the windings.

Put the SBP switch in series to either the black, or blue wire. Then the way it will work is, when the switch is closed, the motor will run. When the switch is open, the motor will kill. The magneto windings will never short, so this should avoid failures.

rohmell · Dec 8, 2012

biknut said:
The stock kill switch shorts the magneto windings, to stop the motor. Shorting the windings is not a good thing for the winding. Magneto coil windings run warm under normal operation. In hot weather, it's possible the extra abuse of shorting the winds may burn them up, causing the coil to go open.

But if you look at just about every small engine made on Earth, used in lawnmowers, snowblowers, weed trimmers, leaf blowers etc, engines made by Tecumseh, Briggs & Stratton, Honda, Robin-Subaru, Mitsubishi, Tanaka, etc., they ALL stop the engine via shorting the magneto to gnd.

Also, look at the old old lawnmower engines that stopped the engine via a shorting bar across the spark plug!

How can all these engines have been designed so poorly?!

2door · Dec 8, 2012

rohmell said:
But if you look at just about every small engine made on Earth, used in lawnmowers, snowblowers, weed trimmers, leaf blowers etc, engines made by Tecumseh, Briggs & Stratton, Honda, Robin-Subaru, Mitsubishi, Tanaka, etc., they ALL stop the engine via shorting the magneto to gnd.

Also, look at the old old lawnmower engines that stopped the engine via a shorting bar across the spark plug!

How can all these engines have been designed so poorly?!

Ditto:
There is no electrical reason why shorting the mag will cause a failure of the windings. There's also an old myth about our engines that is just that, a myth. And that's if you spin the magneto and produce current without a spark plug attached that it will "burn out" the mag. Simply not true.
It is true that electricity will take the path of least resistance. If it finds a route to ground that has less resistance that the circuit it is powering then that's the path it will take. If the insulation on the coil winding is bad or there is a break in it, the current can short to the magneto frame but that would be a rare occurance indeed.

Tom

racie35 · Dec 8, 2012

it'll give you peace

of mind to wire it different.....nothing more

placidscene · Feb 25, 2013

OK, Well, I finally got around to replacing my CDI, and i still get no fire! I thought for sure that was it. Guess I shouldn't have wined about the crappy CDI so quickly.
I opened up the Magneto cover, and it doesn't appear to be burned out, but I am not sure what else to look for.
Any other ideas? Please? Really missing my ride.

BigBlue · Feb 25, 2013

placidscene said:
I opened up the Magneto cover, and it doesn't appear to be burned out, but I am not sure what else to look for.
/QUOTE]

How are going to know if the magneto coil is burned out or has a broken circuit by just opening the magneto cover? You can't. You need to use a DMM and test the circuit. If you rode in the rain or left it out in the rain and didn't properly seal your magneto coil from moisture, it is a possibility the magneto coil is ruined from rust.

Follow the following no-start guideline from forum member AI.Fisherman: https://docs.google.com/document/d/1aBeJuoS--VQWwXysc07rpscTUbPzgc93xjiQBgsyFjc/edit

Also check to make sure your spark plug wire is securely connected to the CDI unit. Some of the plug wires just screw into the CDI unit while other plug wires are screwed and cemented into the CDI unit.

Good Luck,

Chris
AKA: BigBlue

placidscene · Feb 26, 2013

I found that after I posted this link. I will borrow a tester from work tomorrow.
This bike has not seen moisture since I have owned it.

When I bought the new CDI, I also bought a high quality spark plug wire and boot to replace the stock one, I made sure it was on there right when I replaced it.

Thanks for the tips, I will see how it goes with the ohm meter.

placidscene · Oct 29, 2013

OK. So it has been 8 months since my last post! I bought and sold a 1978 Mercedes Coup diesel, a 1967 Chrysler Newport Coup, and a 1991 Jeep Wrangler. Now I am back to my Motorbike project, and would really like to get past this electrical problem!

I did the Ohm test as suggested, and my numbers seemed to be all over the map compared to what was suggested.
Should I try buying a new Magneto?

crassius · Oct 30, 2013

I'd first use a small file to clean the surfaces that transfer ground from the mag to the engine case until the readings are steady. There's no reason for these numbers to change except for bad connections.

placidscene · Oct 30, 2013

OK, Ill give that a shot, When I said my readings were all over the place, I did not have the magneto attached to the motor, so that may have been an issue to. I will re test tonight and record the measurements in a reply here then.

placidscene · Oct 30, 2013

Below are the results of my testing based on the "China Girl Wont Start? Read This" guide.

Defective magneto..testing All readings are approximate.
Use Low Ohm-Meter Scale 200K Ohms

Check Ohms between BLACK wire and WHITE wire. 2 Ohms
I got no reading

Check ohms between BLUE wire and WHITE wire. 300-400 ohms.
I got a reading of .3

Defective CDI..testing All readings are approximate.
Use Ohm Meter High Scale About 200K

Positive lead on BLUE wire and Negative lead on BLACK wire
infinite (no activity)
I got no reading

Positive lead on BLACK wire and Negative lead on BLUE wire.
130-150 K ohms
I got a reading of 63

Positive lead on Spark Plug wire and negative lead on BLUE wire.
135-155K ohms
I got a reading of 76.6

Switch to Low Scale 20K
Measure between Spark Plug wire and BLACK lead. 2.5 - 2.7 K
ohms
I got a reading of 9.05

As I said my reading seem to be all over the place.??

placidscene · Oct 30, 2013

Here is a pic of my tester set to the recommended setting for clarification, and also a pic of my magneto.

placidscene · Oct 30, 2013

I just read the CDI Horror story that is posted below mine.
Wow. Anyway I learned a couple of things I am going to go and try.
Will report back.
Would like to hear someones input on my odd readings with the Ohm Meter though.

My junky CDI went out

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