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Help with hot Stator works

08 Dec 2019 14:51 08 Dec 2019 14:55 by RT360Fan.
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Help with hot Stator works #1
Edit: Lol, title should read "how" stator works...

Hey guys. I'm getting my '81 IT175 back together (finally!) and I was doing some tests on the stator coils. My low speed coil is reading 433 kΩ, should be about 425 Ω. That's way off! All other coils test fine, including the primary ignition coil. Would this cause incomplete ignition al idle/low speeds? Part of the problem is the manual has no diagram of the stator/coils, just measurements. Also, the manual doesn't go into how the various coils effect anything.

Anyway, here is a pic of 1981 IT175 stator/coils. What exactly am I looking at? The manual refers to low speed, high speed, and lighting coils. Which ones are which? Sorry if this is an idiot question. Electrical is not my forte and the manual is a bit lacking on explanation, I would love to gain some knowledge here. Thanks in advance!

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09 Dec 2019 06:21
Fewmarshall
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Help with hot Stator works #2
The coils on the left in the photo are your high and low speed, the single off to the right is your lighting coil.

Now im not certain which is which when it comes to the high speed and low speed coils, but I am fairly certain that the one on top with the black wire is your high speed coil, and the bottom with a red wire would be your low speed coil.

I'm not sure what the resistivity being off would harm

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09 Dec 2019 10:18 09 Dec 2019 11:01 by RT360Fan.
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Help with hot Stator works #3
Thanks @Fewmarshall

I pulled my stator to test the coil directly, just to eliminate any possible issues with the wiring. Yep, low speed coil reads 425 kΩ instead of 425Ω (I hope this isn't a typo in the Yama manual). Looks like time for a stator rebuild... :S

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24 Dec 2019 15:51 24 Dec 2019 15:52 by RT360Fan.
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Help with hot Stator works #4
Sooooo.... I found a new low speed coil, tested at 435Ω which is perfect. Yay, I fixed the problem! Or so I thought... Went out today and started the IT, had an erratic idle, messed around with it a bit but left scratching my head. Just for grins I rechecked the ignition including the stator coils. Low speed coil tested at 435 kΩ. Again.

Everything else tests/checks out fine.

:Ugh

I need to figure out why I'm blowing the low speed coil (These coils are NLA, not easy to find and not cheap). Anyone have any ideas? One thing is I'm not running the lights, I don't have bulbs in the sockets. There is no mention in the factory manual that this would affect anything on the ignition circuit however. Any thoughts are appreciated!

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24 Dec 2019 18:43
MarkT
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Help with hot Stator works #5
I doubt you're "blowing" the coils...

One thing is the resistance changes with temp... manual should spec a temperature at which to take the reading, usually 68 deg F.

Source coils are probably fine and something else is wrong... I'll have to look at the diagrams but most likely the pickup aka trigger coil is acting up?

1963 YG1-T, 1965 MG1-T, Allstate 250, 1970 CT1b, 1971 R5, 1973 AT3MX, 1974 TS400L, 1975 RD350, 1976 DT175C, 1976 Husqvarna 250CR, 1981 DT175G, 1988 DT50, 1990 "Super" DT50, 1991 RT180, 2017 XT250

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24 Dec 2019 21:20 24 Dec 2019 21:26 by RT360Fan.
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Help with hot Stator works #6
Appreciate your feedback Mark, as always.

I know, it's weird. I can't help but think there's a connection between the low speed coil and the erratic idling. Kind of odd that the replacement coil tested at 435Ω (what the manual calls for) on the bench, and now it tests at 435kΩ after running on my bike (which is exactly the same as the original coil it replaced). The values in the manual do not reference temperature, +- 10% of the given value is all. Pickup coil? Is that the same as Pulsar coil? If yes then it passes Ω test. They all do except the recently failed/out of spec low speed coil.

Motor is just rebuilt, both bottom and top end. Holds 6lbs pressure and 6in vacuum for hours. about 125psi compression on my gauge. Carb is spotless and rebuilt with Mikuni parts at factory settings/jetting.

Definitely scratching my head on this one.

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25 Dec 2019 19:12
ajacstern23
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Help with hot Stator works #7
I would be really surprised if a coil failed in that way twice. The most common ways coils fail are going very low resistance if the coating wears off, or they go very high resistance if they fray and get an air gap (at least in the electrical world). Are you sure you are using the right range and have you tried using a different multimeter? Multimeter might be incorrectly turning on the k segment of the display. Have you visually looked at the coil? Any bad solder joints, frays, etc. Pay special attention to the area where the coil wire connects to the mounting tabs, I have had a few break there. You can try warming up the coil with a hair dryer/low temp heat gun and then taking a resistance reading. If you have an oscilloscope try running test wires back through the stator to see what is going on at various points in the ignition. What voltage is the low speed coil producing and that type. You can also look at the spark, should be big and blue. Have you tried messing around with the low speed carb circuit. When you say erratic idle do you mean it is four stroking, surging, missing? Best of luck.
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25 Dec 2019 19:35
RT360Fan
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Help with hot Stator works #8
Good ideas. I thought about my DMM possibly being faulty. My meter is auto-ranging but even if it was reading in the kΩ range accidentally it's not like the reading is .435kΩ. I've had the meter for years and has yet to let me down, although I don't use it a ton. I suppose I could get an inexpensive manual meter as a backup just to be sure...

I'll try heating the coil and take another reading, also reinspect the coil wiring.

On the idle... it's inconsistent. That's the best I can explain it. If I lean the airscrew out too much I start to hear pinging, turn it in a bit (from stock 1 1/2 out) and it goes rich and stalls. Also, when warm, if I lean the bike over on its side stand it will stall. I know, float level, but it is dead on at factory 23.5mm. I keep having to adjust the idle speed screw. One minute it's running fine, then it wants to stall, turn the idle screw in to raise the idle and its fine for a minute, then it will run faster. Fully warm. Inconsistent.

One thought I have is that when I rebuilt the motor I set the stator back to line up with the factory case marks, that seemed to time it correctly as far as the flywheel mark is concerned. I'm going to double check the timing with a dial gauge.

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28 Dec 2019 11:01 28 Dec 2019 11:07 by RT360Fan.
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Help with hot Stator works #9
My plan for checking the timing is delayed, seems like my cyl adapter disappeared so I ordered a new one. Should be here next week (which means that the old one will magically appear .5 seconds after the new one arrives lol).

So I ran the engine again to try and sort out the idling issue and it seems that the motor is running really rich (carb=stock settings/jetting), and something new... I noticed fuel leaking out of the exhaust/cyl junction. So since I'm waiting anyway for the dial gauge adapter I decided to inspect the top end. Everything looks OK visually. I checked the ring gap according the the factory manual, tolerance 0.2mm-0.4mm. End result of my measuring is that a .5mm feeler goes and a .55mm doesn't. Seems the ring gap is out of spec. This is a fresh bore with less than an hour on it.

I regret not checking the ring gap initially when I installed the fresh top end. I assume this means I need another bore?

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28 Dec 2019 16:20 28 Dec 2019 16:22 by RT360Fan.
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Help with hot Stator works #10
OK, to circle back to the stator coil, I did as ajcstern23 suggested and checked it with another DMM. The coil test passed, it's good. I feel like a complete idiot!

Now I have to figure out why it's running way rich.

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