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Discussion Starter · #1 ·
This is the same 1987 TW200 with other posts, but thought I should keep the different topics separate. Moderator, if not correct, let me know and I'll combine them.



In my quest to solve my issue and eliminate everything I can, I removed the left engine magneto side cover to make sure the wires that exit upper rear hadn't been pinched. No sign of that.

I measured the magneto's Pickup and Source Coil resistance at the plugs by the CDI Unit.

Pickup Coil (G-W wires) was 831-835 Ohm over multiple measurements. Spec is 650-790, so its technically out of spec.

Source Coil (Br-R wires) was 403-405 Ohm over multiple measurements. Spec is 400-450 so its within spec.

Is the Pickup Coil measurement enough to indicate a problem? The temp measurement is supposed to be at 68F temp and the garage was at 51F. Not sure if that's much of a game changer or not.

Also checking grounds and tracking through the wiring to see if I can find anything.
 

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Stator readings are notoriously difficult to pin down, unless you read zero. I know what the "book" says, but it's rarely that easy - (and yours is not that much out of spec)

The '87 is notorious for dumping the CDI, another part that is tricky to fault trace

The simplest way out of this, is to let us know your location, and if possible, find another rider to swap out the CDI with. If you have 250 bucks to spare, Waterloo CDI's can accommodate the '87, but I'm unsure of their returns policy for electrical goods if it doesn't prove to be the problem part - worth contacting them to see what they say, the proprietor, Tom Bauer, is a member on here so it's all "in house"

There will be a bunch of people along soon to recommend sticking your CDI in the freezer, and clamping it in a pair of vice grips, but that stuff is just as hit or miss as your original problem

The Chinese CDI's advance curve is not up to the job, so although they will get you home on a rainy day, best used as a paper weight

Although the CDI hasn't changed much over the years, the wiring has, so try to check it with another '87 if possible - but I'd try Waterloo CDI's as a starting point - Your source for new CDIs for old Yamaha products
 

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Discussion Starter · #3 ·
Thank you, all good info to know.

I have tried another 87 CDI loaned and mailed to me by TW-Brian . Also tried the freezer trick and a good wack with a wood handle.

Haven't tried the clamp test - just ran across a post where someone here twisted a wire tightly around the CDI with large washers under the wire. I'll try that after I get the stator cover back on. If I can see a change (even temporary) it could pinpoint the issue.

I have no problem buying a Tom Bauer CDI or a carb conversion. Just trying to isolate the actual issue before throwing a few hundred bucks into it.

The thing that gives me pause on the CDI is the known good CDI didn't change anything, yet my wife's description of what happened sounds electrical more than carb since:

A) it happened suddenly

B) there was one time where it suddenly acted normally for about 2 minutes then just as suddenly went back to its weak running state.
 

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You have checked the intake, how about the exhaust. A plugged exhaust or carbon encrusted spark arrester is worth checking on a 36 year old bike.
I get sluggish and hard to start when my exhaust gets plugged.
 

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Pickup Coil (G-W wires) was 831-835 Ohm over multiple measurements. Spec is 650-790, so its technically out of spec.
If your meter reads zero ohms with probes touching together, the measurement is only over spec by <6%.
That can happen if probes do not make good contact and/or internal coil connection issues.
Most likely NOT an issue.

If the measurement were low, that could indicate a partial winding to winding short in the coil.
 
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