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Discussion Starter · #1 ·
I'm on the verge of spending money and buying coils, but before I do, I'm looking for a way to definitively telling if my existing ones are bad.

I don't want to pour any more money into this piece without KNOWING it's for the right thing.

So how do I test my coils/condenser, and please spell it out to me like I'm an elementary school kid, LOL...

-MK
 

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There's no way to really test either of those things, unless you have access to some pretty expensive diagnostic stuff. A couple of fairly meaningless ohm readings is about all we can do.

My input - if the bike runs good, why worry about it??

Generally, it's never a bad idea to replace 40 year old electrical stuff, though.
Coils are cheap, so are condensors.
Condensors have a limited shelf life, even when never used.
And coils can drive you nuts, they tend to glitch when they get hot, at the most inopportune times.
 

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Discussion Starter · #3 ·
I would love to take your advice, however my bike isn't running, and I'm getting a weakish white spark on the jug that's not firing. Plugs are good, etc.

Guess I'm going to pony up for coils/condenser.

-MK
 

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MK, My advice at this point would be to get some new coils from Mike's XS....... You surely don't want to be pushing the bike home from somewhere, and a "static" test will often NOT show a problem that develops when the coils get "hot"........ A new condenser is ALWAYS a good idea, they can go "bad" just from age and sitting........
I'd be happy to send you a "loaner set" of coils for testing purposes, but really think you should opt for new at this point....... Steve

I see Bill beat me to a response, but maybe a consensus of opinion will verify the need to replace.......
 

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Discussion Starter · #5 ·
There's a local place here in Columbus that sells vintage japanese bike parts. They have 2 huge warehouses full of old bike stuff:

http://www.ricepaddymotorcycles.com

I called and they have a set from a CB360. I'm going to run down there tomorrow and pick them up. If that solves the problem, I'll go the MikesXS route. Hopefully my used set will last the remainder of the riding season. I also picked up a NOS condenser on eBay (although if they have a shelf life, I wonder how good it will be). I'm also going to work on the timing again tomorrow morning since I couldn't get it perfect yesterday. I swear doing timing correctly on these bikes is INFERIATING!!

Thanks again.

-MK
 

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mktsc said:
I would love to take your advice, however my bike isn't running, and I'm getting a weakish white spark on the jug that's not firing. Plugs are good, etc.

Guess I'm going to pony up for coils/condenser.

-MK

Make sure your battery is strong first - can it turn the electric start easily??
If not, don't do anything about seemingly weak spark until you correct the battery problem......
 

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Discussion Starter · #7 ·
Yes, the battery turns the electric start easily. I have it on a tender. Furthermore I get a nice spark on the RH cylinder, andit tries to run on one cylinder. I think it's probably part timing and part bum coil on the LH side.

Will update tomorrow.

-MK
 

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I'm not familiar with the 360 but if you know one side is working fine why not just swap coils and see what happens. You'll have to physically move them but that should be a big deal. If the problem changes sides then you'll know you've got a coil problem. If it's still a problem on the left side then you'll know you've got another problem.

Remember, ONE thing at a time. Don't do both the coil and the condensor. One thing at a time.
 

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Well, I'm probably going to start an arguement with this, BUT... The condensers have nothing to do with the spark to the plugs.... They are in the system to protect the points..... The coils would work fine (possibly even better) without them in circuit....
I'll go into the full explaination...as it was told to me ( lo these many years ago)....When I have more time tonight....... Steve
 

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Discussion Starter · #10 ·
Steve I've heard the same thing. It was explained to me once, but I forget exactly why. In any event as stated above, I do not want to modify more than one variable at a time. I'll do coils and timing today.

-MK
 

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The condensor is, indeed, there in part to protect the points.

When the points are closed, current is flowing thru them (and thru the coil first) to ground. When they open, that current flow stops, but while they are just barely open (think microscopically), there is certainly enough potential to jump that tiny gap, ie a spark. Think of it as drawing a tiny little arc like an arc welder. Now, that spark is still current flow, and the whole point of opening the points is to STOP current flow so that the resulting collapsing magnetic field in the coil's primary winding will induce a current in the secondary windings enough to jump the spark plug gap - spark the plug.

In addition, that little spark at the points will eventually burn their surfaces up.

The condenser serves to 'absorb' that momentary voltage surge at the points until the air gap is sufficient to block a spark.


As for troubleshooting a weak spark on one cylinder, I'd be certainly swapping parts side-to-side as mentioned. Spark plug, ignition coils, condensers, etc. And only one component at a time, of course. That way, you'll KNOW which component may or may not be bad.

And, timing difficulties won't cause a weak spark. They'll only cause the weak spark to happen at the wrong moment. A different problem, which of course needs to be fixed, but not the cause of a weak spark.

Good luck, and keep us posted.

Kirk
 

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Don't forget to check resistance at the spark plug wire caps- They go bad frequently and make you think the coil is bad. They just screw onto the coil wire. Unscrew and check- more than 6 ohms resistance and they're toast. If you have the room on the wire cut a quarter inch off the end of the coil wire before you screw the cap back into it- another place corrosion and resistance can build up. Just thinking of things that have happened to me. Good luck!
 

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Discussion Starter · #13 ·
Ok, I've just finished up for today. I got a replacement coil, but have not installed it. I wanted to make sure I had my timing dead nuts before I moved on. It took me 3 hours, and I had to use a rat-tail file and widen the slots in the LH points arm, but my gaps are dead nuts, and I get the points to open at EXACTLY the right moment.

Here's the thing. I'm using a multimeter set to VDC to do the static timing. I usually read 12VDC or so while the points are open, then about 200-400mv while the points are closed. I was able to repeat this until about the last half hour of adjusting, where open or closed, I read 12V for the entire rotation and didn't get the spark at the gap on the LH side. I had the battery plugged into the tender the whole time, but I'm wondering if the battery was sufficiently drained not to provide a spark. The thing is, the LH side is the only one that's not firing. The battery still has enough charge to turn the electric start, but I'm wondering if gets to a certain level of charge, and the LH coil is the first one to not fire, and that's the point I'm at. I'm sure the points are opening and closing all the way (making sure is why it took me 3 hours to time the bike).

So I'm going to fully charge my battery, and then see if I get spark. If not, THEN I'll install my replacement coil (which I witnessed being tested 'good' while I was at the shop). I only got the LH coil because if that was the actual problem, I'll do a full coil upgrade. The replacement used coil was only $20 though.

I'm so close I can taste it, and I think it's going to run beautifully once I get the spark figured out.

What do you guys think about my hypothesis?

-MK
 

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If your meter constantly measured 12 volts across the points, they never closed. Go back and do 'em again.

Think about it: you have 12 volt potential on one side of the point, ground on the other. Points open = 12 volts on meter. Points closed = conductor = no voltage on meter. A meter measures the voltage DIFFERENCE between two points. There is no (appreciable) difference between two adjacent points in a single conductor.

Go back and reset the LH points. Yer not done yet.

And 3 hours?? You're overthinking it. Despite what Bill sez - it AIN'T that critical for what you're trying to do (troubleshooting a weak spark) :mrgreen: :mrgreen: .

Kirk
 

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Discussion Starter · #15 ·
I physically closed the to where I put pressure on the spring and physically moved the phenolic points arm and still didn't get the voltage to change.
 

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So you have established that your points are "burnt" (or obstructed) to the point where they no longer conduct......If they don't conduct, they don't ground...If they don't ground, the coil won't charge..... If there's no "charge" to collapse, No fire at the plug....
 

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Yep..... Especially IF they have been "cleaned" with emery cloth or paper...the emery impregnates into the point material and it no longer conducts.......
 

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<Thread Jack> Steve, you mentioned getting replacement coils from Mike'sXS. Are they interchangeable or bike specific? Just wondering...
 

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AFAIK... They are just 12V Yamaha "point" type coils..... Yamaha did make two sizes but either will work electrically....... The smaller XS 400 size might be easier to "fit" to the bike.... Bill2 is using some on his 450 (not sure which) so maybe he has a specific part number somewhere in his build topic.....Tell the guy at Mike's what you'll be using them on....
 
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