Help me find spark on my SR500

scott s

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I recently picked up a 1980 SR500 that's been off the road for years: http://www.dotheton.com/forum/index.php?topic=75801.0

I can't get spark for the life of me. I did the test procedures from Rex's Speed shop.

https://drive.google.com/file/d/1ds48JON5ZCEoU92-dm269MFteAf1Pj-t/view

Initially, the only thing that came back wonky was a very HIGH reading on the coil secondary. Usually low or open is bad. Either way, ordered a new coil from Rex's. This is the proper 1 ohm coil with proper grounding for CDI, etc.

http://www.rexs-speedshop.com/epages/es143131.sf/en_US/?ObjectPath=/Shops/es143131/Products/HTC10

Installed that and still no spark. The test procedure tests the wiring going TO the CDI, but there's no way to really test the CDI. So, I ordered a new CDI from Rex's. Still no spark.
I've gone through the test procedure twice more. I've done it with and without a battery in the bike (the SR500 will run without the battery. The battery has nothing to do with the ignition). I can't find anything wrong.
One slight oddity, and I don't think it's an issue, is that my Radio Shack meter reads on a 200 ohm scale, then goes to a 2K ohm scale. Some of the stator windings are supposed to be 330 ohms. I use the 2K ohm scale and get readings with a decimal in front. BUT....isn't .330Kohms the same as 330 ohms?
Rex's is telling me to sort out the issue with the meter, but if I understand it correctly, those readings are good.



-I checked that the stator and flywheel are matched. They are.
-Tried a new plug and the old plug.
-Pulled the sprocket cover and checked for frayed wires from the stator (even though tests are good). Found nothing.
- Checked from the coil to the CDI and get the same 0.9 ohms (good).
- Tried unplugging the kill switch. No spark.
-Checked the gap on the pickup and got .030-.032, so good.

And on and on and on. What next? Why don't I have spark?
 
I tested the kill switch.
I have continuity from the connector in the harness all the way to the CDI plug on both the Black and Black/White wires. I get 0.9-1.0 ohms on those wires.

I tested the operation of the switch itself and I get:
OFF 0.4 ohms
ON Open, or infinite
OFF 0.5 ohms

I tested the key switch, going from the Black to the Black/White in the 4 prong plug.
OFF 0.2 ohms
ON Open, or infinite.

I am pretty confident at this point that I do not have a broken wire anywhere in the wiring harness. EVERY test that I do tests good, at least to the best of my ability. I'm stumped and frustrated.
 
I never had an SR. I did have an SRX which had a habit of losing the spark, I don't know if your SR came with a sidestand "kill" switch. The SRX had one. If you do have a sidesatand switch take a look.
 
Bumping this up because, guess what? I *STILL* have no spark!

After testing, testing and more testing, I sent it to my friends shop in Charlotte. He's had it for a few months now (he's mostly European bikes these days, so I was thankful he'd take a look at it) and he can't get spark either.

His tests on the stator came back bad/low. I may have missed that because I was using a cheap meter and my scales jump from 200 oHm to the kilo-oHm scale.
He sent the stator to Rick's for a rewind. When it was returned, one of the pick-ups was hitting the flywheel. Sent it back to Rick's and they fixed it. Still no spark.
My mechanic has traced out the entire harness, just like I did, and found nothing. Tried removing the B/W wire from the CDI (it grounds the spark, killing the engine) and that didn't work, either.

We confirmed that I ordered the correct CDI from Rex's (I did). We asked Rex's to test both the old and new CDI units but they declined, saying that taxes, import duties and fees make it not feasible.

-New correct coil from Rex's (includes cap)
-New plug
-New CDI
-Stator rewound
-Harness and controls checked
-Confirmed stator/rotor/flywheel match
-Confirmed rotor has't spun on the crankshaft
-Checked, tested and cleaned multiple grounds

Now what?
 
If the CDI is a spark box like on the DOHC Hondas, it sounds like you've gone through every thing but the ignition system itself.

Charging system shouldn't be the cause of no spark, until the battery is drained.
 
I've gone through the ignition system. The coil/wire/cap was replaced with a brand new, correct coil from Rex's. The CDI was replaced with a brand new, correct unit from Rex's. That stator was rewound at Rick's.

And, correct me if I'm wrong, but the battery isn't needed to make spark on an SR500.
 
I believed a battery, or capacitor, is needed. Though, I could be wrong as well.

Certainly sounds like a head scratcher. Hope you get it sorted.
 
Have you tried removing the plug and checking the spark with the bike in high gear and spin the rear wheel ?
sometimes the magnetic field is weak and the kick starter cant spin her fast enough to throw a spark..push starting can sometimes work....
also have a look ere maybe there is something that will help
https://yamahaclub.com/forums/topic/8213-78-sr500-no-spark/
 
As I understand the system there's two connectors from the stator. One with white wires is the battery charging, so we can ignore that. The other connects to the CDI and includes connections from the charge coils and the pulse coil that tells the CDI to fire.

The CDI has another connector with 3 pins that goes to the coil but also connects to the kill/run switch. I would try to connect a matching connector with just 2 wires to the coil and patch that to the coil to temporarily eliminate all the other wiring and then spin the rear wheel fast to check for spark.
 
Sonreir said:
Sounds like you've replaced everything except the coil, is that correct?

No, the coil is new, from Rex's.

This one: https://www.rexs-speedshop.com/product/htc10-sr-xt-tt-400-500-600-ignition-coil/

I tried initially with the old coil. I trimmed the wire back and installed a new cap and plug. When that didn't work, I ordered a coil from Rex's.
When the new coil didn't work, I got a new CDI from Rex's.

This one: https://www.rexs-speedshop.com/product/sr400-sr500-cdi-unit-1979-97/

When that didn't work, I did these tests here: https://www.rexs-speedshop.com/wp-content/uploads/2018/10/Yamaha-SR400500-Ignition-Testing.pdf

I can find no fault with the wiring harness or controls. I checked all connections. I checked the harness from end to end and with each component/section. Checked grounds.

Gave up and sent it to my buddy's shop. With his better meter, he diagnosed a bad stator. Sent the stator to Rick's for a rewind and it still has no spark.
Confirmed stator, rotor and flywheel match. Confirmed flywheel/rotor hasn't slipped on crank.
 
teazer said:
As I understand the system there's two connectors from the stator. One with white wires is the battery charging, so we can ignore that. The other connects to the CDI and includes connections from the charge coils and the pulse coil that tells the CDI to fire.

The CDI has another connector with 3 pins that goes to the coil but also connects to the kill/run switch. I would try to connect a matching connector with just 2 wires to the coil and patch that to the coil to temporarily eliminate all the other wiring and then spin the rear wheel fast to check for spark.

OK, thanks for the suggestion. I'll relay this to the shop.
 
wozza said:
Have you tried removing the plug and checking the spark with the bike in high gear and spin the rear wheel ?
sometimes the magnetic field is weak and the kick starter cant spin her fast enough to throw a spark..push starting can sometimes work....
also have a look ere maybe there is something that will help
https://yamahaclub.com/forums/topic/8213-78-sr500-no-spark/

I have not tried that.
I have wondered about the magnetism of the rotor. When I touch a screwdriver or allen wrench to the rotor, I can feel a slight tug, but not strong. I've worked on a few CB/CL350's and the rotors on those bikes are strong enough to grab a wrench or screwdriver.

If the magnetism is weak, what can you do about it?
 
scott s said:
If the magnetism is weak, what can you do about it?
There are a few places that can re magnetize em google prob the way to go, if there are magnets bonded to the flywheel these can be replaced....prob easiest to find a nos unit or better 2nd hand replacement....But first you need to sort out if thats the issue :D ...It tends to be heat that ends up killing the magnetization, lots of hot runs/heat cycles over many years or owners using a blow torch to heat up the flywheel to remove it
 
Relayed a few of these suggestions to my mechanic. He says he did try turning the rear wheel in high gear.

He's going to look into the magnetism thing. He works on old Triumphs and has seen them charge like shit when the rotor gets weak.
 
In top gear the motor turns slowly. He needs to try second gear with the plug out.

Loss of magnetism could certainly be an issue.

Did he try for a spark with the coil wired directly to the CDI - that would identify any shorts in the kill side of the circuit.
 
I'm not 100% sure of what all he's tried, but every time I relay these suggestions, he says he's tried it. He's a pretty good mechanic.
I tried turning it in 2nd gear at home, before taking it to him.

I'm beginning to suspect the flywheel. I noticed when working on it that the magnetic field is weak. It barely pulls on a screwdriver or Allen wrench and is certainly NOT strong enough to hold one firmly.
My mechanic has had the flywheel off to replace the stator, but I haven't. I don't know how strongly it pulls when replacing in on the crank/stator.

I found this online:
"Have you considered the possibility that the magnets on the flywheel may be weak or lost their field?
If the unit has been dismantled for any decent period of time and left separated,the field may have degraded.
It used to be recommended to either leave a flywheel magneto all together or put a bar across to preserve the magnetic field.

Good magnets should strongly and quickly pull a spanner held in your hand onto themselves and be a bit difficult to remove it.

Weak magnets will result in a weak and erratic spark.
"

Mine is NOT that strong, from what I remember. I've worked on some CB/CL350's and the rotor on them is strong enough to pull and hold a wrench. My SR500 is NOT.

If the flywheel has lost its magnetism, then what?
The parts fiche lists the flyhweel/stator/magneto as a unit. Even IF I wanted to find a used one, I'd have to make sure it matched my stator, and then there's no guarantee it's good.
Is there a way to re-magnetize the flywheel? Are there any shops in the US that can do that for me?
 
Sent these guys an email to see if they can do the SR500 flywheel.

https://www.scooterwest.com/flywheel-re-magnetizing-labor-remag.html
 
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