YFM225 Trigger wire from magneto

332 Views 14 Replies 3 Participants Last post by Chromakey, 13 d ago

Chromakey

Discussion Starter · 27 d ago

Hello all, I have a YFM225 from 1987 and I believe the CDI has died so want to replace it with a DC CDI. I have the circuit diagram for it with the colour codes from the magneto but it does not actually say which one is the wire for the trigger - there is black which I think is the universal 0 Volt rail, Brown, White/Red and White/Green. Does anyone know which of those is the actual one for the trigger pulse?
Thanks

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Mech

· #2 · 27 d ago

If you check the resistance of the coils in the stator and trigger coils you will find that the stator windings have a low ohm reading, probably between about point five and one ohm, and the trigger coil will have higher ohm reading, probably between about sixty and two-hundred.

If you have the service manual it will tell you exactly what the readings should be.

I'd reccommend you test and verify the cdi unit is crook before spending money that might not fix the problem.. Like.. have you tested the kill switch, and checked the wiring for breaks or shorts ? A manual will tell you how to verify where the problem lays..

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Mech

· #3 · 27 d ago

It's not the same motor but I think the specs and tests will be very similar..

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Chromakey

Discussion Starter · #4 · 26 d ago

Mech said:
If you check the resistance of the coils in the stator and trigger coils you will find that the stator windings have a low ohm reading, probably between about point five and one ohm, and the trigger coil will have higher ohm reading, probably between about sixty and two-hundred.

If you have the service manual it will tell you exactly what the readings should be.

I'd reccommend you test and verify the cdi unit is crook before spending money that might not fix the problem.. Like.. have you tested the kill switch, and checked the wiring for breaks or shorts ? A manual will tell you how to verify where the problem lays..

Thank you for the help - I only have the circuit diagram so will go by the readings you suggest. I have CDI's here anyway so not a problem.

Chromakey

Discussion Starter · #5 · 26 d ago

Mech said:
It's not the same motor but I think the specs and tests will be very similar..

Thank you very much - I hope to sort this quickly now.

Mech

· #6 · 26 d ago

No trouble..

Chromakey

Discussion Starter · #7 · 25 d ago

Mech said:
No trouble..

Initial checks using the data sheet you provided would appear to show that the trigger coil is open circuit so I will take the cover off and check more fully. I can get a new coil so that is not an issue if it proves to be so. I am also lucky that I have a couple of laser engravers so I am able to cut new gaskets and have already started work on the artwork for one that just needs scaling down from the oversize I have now. I have not lost anything because I had spare CDI's anyway and it is better to keep original if I can than having to modify if I don't. Thanks again for your assistance.

Mech

· #8 · 25 d ago

Loctite master gasket.. throw those gaskets away.. haha.

It's always worth inspecting the wires at their ends where they go into their metal terminal that goes into the plastic plug. That's where most wires break.. The open circuit isn't always right inside the windings.. Flex the wires gently one at a time rightwhere they go into the terminal and you might feel the broken one is floppy..

Chromakey

Discussion Starter · #9 · 24 d ago

Mech said:
Loctite master gasket.. throw those gaskets away.. haha.

It's always worth inspecting the wires at their ends where they go into their metal terminal that goes into the plastic plug. That's where most wires break.. The open circuit isn't always right inside the windings.. Flex the wires gently one at a time rightwhere they go into the terminal and you might feel the broken one is floppy..

Are you casting aspersions on my gaskets?

I definitely will check the wires out for breaks before committing to buying a new coil as I am always suspicious of these types of faults and finding weak spots on cabling.

Mech

· #10 · 24 d ago

Your cutter sounds like fun, and I have no doubt it makes very nice gaskets, but I just prefer loctite.. it's way economical, clean, never hardens in the tube, doesn't block selves, the assembly proceeds uninterrupted.. Try it, you'll like it.. haha.

Yeah cdi are too dear to buy if we don't need them.. and so are stators ! Too many people throw parts at bikes without even checking the wiring.. Wiring can get breaks, so we need to check them from end to end, They can get dirty where the wires crimp into the terminal or where the terminal contacts the unit, and they can get shorts to the frame, sometimes intermittently, so we need to inspect the wiring for chafed insulation.

If everything is good, then you can use some other cdi unit if you are conversant with the different types and how they work. The most common modification that's needed to use a different unit, providing it is suitable, is that the windings need their two wires flipped over where they connect to the cdi unit. Either the trigger or charge wires can need flipping.

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Foot0069

· #11 · 24 d ago

Wow the laser giz is the bomb. Mech, I'll be trying your master goop as they sent me the wrong gasket for my crankcase cover. The buggers. 😀

Mech

· #12 · 23 d ago

Bugger alright.. specially when you live out of town , and don't like town, and don't go there unless there are several needs..

Check the clearance is ok without a gasket.. most things are.

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Chromakey

Discussion Starter · #13 · 20 d ago (Edited)

Automotive tire Gear Motor vehicle Bicycle part Rim

I have managed to get the outer housing off including some persuasion with an impact driver for the more stubborn M6 bolts. Now got the thing apart and can confirm that the trigger coil is open circuit (measured at the joints inside the housing around the stator) New one about to be ordered!

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Mech

· #14 · 19 d ago

Good work.

Chromakey

Discussion Starter · #15 · 13 d ago

So many people never follow up in forums on what happened to them with their problems but I thought I would say that the replacement pickup coil arrived a little while ago today and I fitted it. The engine now fires so just have a flat battery and a leaking float bowl to deal with (rather odd as I did drain it down before leaving it) but at least now the engine is working again!

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