Hi XT wizards

EDIT: updated title as wiring looks ok for now.

I built a scramberified XT600 for our daughter and did good 5000km on it before she was old enough to get a bike license.
However, 2 days before she was due to get her license, XT lost the spark.
I stopped after a short ride around paddocks, left bike idling for about 1 minute when it suddenly just died.

Symptoms: cranks fine, just no spark
Problems ruled out so far:
- Kill switch
- Side stand switch
- Ignition lead
- Spark plug cap
- Coil
- CDI to ignition coil continuity

Still to check:
- Clutch switch
- All connections etc.

I suspect this is caused either by corrosion after recent 1700km trip out of which 230km was along beach or by steering head bearing change while handlebars, including all wirings were hanging awkwardly upside down all over the show, possible kinking the wiring somehow.


Anyhoo, while trying to figure out what inputs CDI needs for allowing spark, I noticed a bit weird voltages in CDI connector.
Could somebody please measure voltages in CDI plug wires with ignition on, ready to start.

It's 3TB model CDI like below.
So far I get 12V only on top left wire of right hand plug whenever ignition is on. Should any of the other wires have any current?

Another odd finding was on wires going to side stand switch.
With ignition on, blue/yellow wire has only 4.5 volts? What's the deal with that? I was expecting to see 12V?

Well lets call it by its correct name, its not a CDi its called a TCi (Transistor Controlled Igniter) as opposed to a capacitor discharge ignition.

Mezo.

i dont see in your list a check of the signal pickup, do it too

Hi, here are some diagrams that might help.

Ok, XT is starting to scare me now.

Wiring looks ok, thank's dblunn for diagrams, ignition pickup and coil check out fine too.
Then the dodgy bit; Even though I'm getting spark, bike does not start and just give few random backfiring pops while starting.

So I ended up pulling the spark plug out once again, grounded it and hit the starter. Got nice spark as expected.
Then I thought to do a simple, rough ignition timing check by turning the crankshaft with socket wrench and waiting for a spark in relation with timing mark.

Problem is that I don't get spark at all when turning the crank by hand??

guess you grew up on points ign, but on modern bikes the signal pickup will not generate a pulse at hand rotation speed. you need a strobe gun to check timing using the starter motor or kick

timing would be the last of my worries, there is no adjustment in these systems and they cant go out of sync.. unless you broke the key for the rotor and it spun on the shaft. very unlikely but a 25 dollar gun from ebay will confirm

I'd also suggest the simple fix of trying a new sparkplug. Several years ago (on Yamaha 660 by coincidence) I had similar symptoms. After stripping and cleaning the carburettor half a dozen times I found I had a dodgy sparkplug. Like yours the original one gave a nice fat spark when removed and grounded, but for some reason can't have been doing this under combustion pressure. A new plug and she ran beautifully.

(I've read of others having similar experiences with plugs breaking down under combustion pressure. I can think of no logical reason why this should happen. If any one has the explanation I would love to hear it)

Sent from my Moto G (5S) Plus using Tapatalk

__________________
Martin

finally back on the road again


http://awayonmybike.blogspot.com/

Found the problem.
It was coil, even though ohmmeter measurement was in specs.

I got the spark back but bike had all the symptoms of too advanced timing. Fortunately I had a spare coil from my old -68 Fiat 500, plugged the car coil in, hit the starter and bike fired up immediately.

I am curious to what the Ohms testing shows on the ignition coil you said was bad and compared to the new one.

I recently bought a new one off ebay, also a new CDI. On my first ride 10 miles in once I tried to open her up past 55MPH she putz out and died and could not get her running again. I found out I have no spark again. I checked the pickup and it was showing 113Ohms and source coil was showing 188 Ohms. Based on a 1985 xt600 manual from Clymer, it was within spec. Hopefully its the xt version and no one replaced it with a TT version because then max on the source coil would be 170 Ohms.

here is the specs for thr 1985 yamaha xt600 from the manual.

Pickup Coil
White Red -to- White Green connectors..................... 90~120 Ohms (My reading was 113 Ohms)

Source Coil Resistance
Red -to- brown wire connectors.................................. 160~240 Ohms (my reading was 188 Ohms)

Ignition coil
Primary..............0.27~0.33 Ohms
Secondary.........3.44~5.16 k Ohms

Anyways back to the ignition coil. mine is reading...

Ignition coil
Primary..............0.51 Ohms
Secondary.........2.78 Ohms


I think I need to replace my ingition coil again.

What ya'll think?