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Discussion Starter #1
Does anyone know the primary resistance specification for stock CB 450 (1974) coils? Haynes and Clymer just say to compare the two coils, and the factory manual says to use the factory tools. Both of mine are reading 1.6 ohms, which sounds low, based on the fact that most people here say 3, or 4, or 5... But if the difference between 3 and 5 doesn't matter, is 1.6 a big deal?
The bike starts on one kick but only on the left cylinder (compression's 165/158, valves are great, fuel's getting through, points are set, condensor's new), but the right side fires about once every three days. I'm about good enough with electrics to be happy I haven't yet electrocuted myself, so ANY help (even advice on which replacements to get) would be really appreciated.
 

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that sounds low, low coil resistance is really going to tax your charging and points systems.. (lower primary resistance raises current use) Have you pulled off your plug caps and inspected them? they thread onto the end of the plug wires, take em off, cut the plug wire back about 1/2 " and re thread the caps on the wires.

Just for gee whiz have you swaped spark plug and coils side to side? (plug the yellow points wire into the blue coil wire and the blue points wire into the yellow coil. plug the right coil into the left spark plug and vice versa, if the problem stays with the right calendar then try it with the points cover off, some points arc on the cover and need a second gasket to keep the cover from grounding out the coils. if the problem moves with the coil then you might need a new one.

As for suitable replacements, any 3-5 ohm coils you can mount securely will do the trick xs650 coils are popular easy to mod the mount dyna coils are good, but they are proud of them
 

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Discussion Starter #3
Great! So I did all of those things, though unfortunately not one at a time so I'm not entirely sure what did it. The short story's that it worked - sorta. I started by retesting the coils and, though they'd been off the bike for a few days the last time I tested them, they were 1.6 ohms then and now they're both about 5.0 ohms. I tested them a bunch of times. I don't know what's going on there, other than maybe it was 20 degrees warmer last week and I replaced the battery in my ohmmeter.
But so they read 5.1 ohms. I swapped sides, removed the points cover, replaced a bunch of the wire connectors along the way, cut an inch off of both plug wires and they both had spark. The coil that wasn't sparking, now on the left, looked a little weaker than the one on the right, but at least it was firing.
I put everything else back together and went to fill up the tank, and it went right up to 75 on the freeway without a hiccup. I got it home, after about 5 miles, readjusted the fuel screws and was checking the voltage output when it quit (it idles at 14.5 volts and topped out at about 16 volts). I'd let go of the throttle at about 6k rpm and it stalled. And once it quit, it wouldn't start, and wasn't showing any spark.
I've heard coils get problems once they're hot, and I'm sure 5 minutes of idling had it pretty warm, but is it possible that they had enough in them to keep it running but not to re-start it 30 seconds later?
I'm going to see if it starts once it's cooled off for a few more hours, get it hot, and then re-test the coils as quickly as I can. Yes?
First time its been to highway speeds in 3 months, though, so that was great!
 

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Discussion Starter #4
New question - does it seem like a hot pair of coils might have gotten to a point where they drew so much current that they'd blow a 15 amp fuse? I went back to it, having let it sit overnight after it had stalled and wouldn't start again, and there was absolutely no power even though I had it on the battery tender, so I checked the fuse and it was blown. I replaced it, and the tail light wouldn't work - the brake light filament was good, and the headlight came on with both lows and highs, and the tail light would come on with the ignition switch in the park position, but the tail light was out when it was running and the headlight was switched on. i jiggled the round connector upstream of the ignition switch and that fixed it.

Maybe the fuse is a coincidence, but I'm not sure. both coils are firing, its running right up to 75 or 80, and I can't get it to die again. I'm not sure how hot the coils need to be before they give out, but I don't want to be 20 miles away from home if/when they finally give out, and I can only drive around my neighborhood just so many times... I'd like to avoid buying the new coils (even at $25 per from MikesXS) if I can, but now I don't trust them.

Guess my plan is to carry a box of fuses and hope for the best. But - thoughts on the fuse? Anyone?
 

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This may be a little late, but when you first tested the coils and got 1.6Ohms, did you disconnect the coils from the ignition circuit? I'm not sure of the proper procedure for testing ignition coils, but if it was still connected to the circuit, you could have been measuring the resistance of the coil in parallel with whatever else might be in the circuit, which would cause a lower than expected resistance reading.
 

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First, to Donny...... Reading through "extra" parts/wiring would increase the resistance.

Second, to JD.... Leaving the key on can heat a coil enough to fry a fuse (and/or weaken the coil or kill the battery), but an overheating fuse is often from using a SAE fuse in a metric holder....
 

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Discussion Starter #7
Thanks both. These both look like opportunities for questions I should have asked a long time ago.
Before that, though, I can report that I'm pretty sure the fuse had nothing to do with the coils; I later identified an intermittent short to ground at the harness hookups for the starter solenoid, which I'd removed when the starter died. The hotwire there was bare and I must have touched it to the frame when I had my voltmeter hooked up to the battery.
As for the resistance on my coils, I definitely had everything disassembled and was checking them on the bench. I even had them separated from the bracket. So as sure as I am that they once read 1.6 ohms, I'm just as sure now that they've been reassembled and working more or less fine for the last 4 or 500 miles. I'm about to winterize and will have a long winter to think about it, but I'm guessing that the periodic misfire was fixed by a combination of my swapping in a different condenser, cleaner connections throughout and better spark plug cap connections/shorter plug wires. One way or another, it all seems at least okay enough now to worry about bigger problems.
My first question - regarding electricity. My highschool physics memory is that the total resistance for a circuit wired in series will be the sum of the resistances of individual components, while for a circuit wired in parallel will have a total resistance equal to the inverse of the sum of the individual components. I'm not sure that this is relevant here, but I'm curious, and maybe someone can clear it up? The question: does wiring in series give you a higher total resistance and wiring in parallel give you a lower one?
Second question - I've seen the posts on metric - v - SAE fuses and thought many times about needing to get the right ones (which I haven't). So where does a person buy these metric fuses? If it's not a show bike, does it make sense just to swap in a different fuse holder? I can't seem to find anything other than regular buss fuses...
 

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My highschool physics memory is that the total resistance for a circuit wired in series will be the sum of the resistances of individual components, while for a circuit wired in parallel will have a total resistance equal to the inverse of the sum of the individual components.

That's essentially it - but it can get complex, you're not just dealing with a resistor, you're dealing with all 3 traditional electrical "components" (resistor, capacitor, coil) all at once.
The "capacitive reactance" and "inductive reactance" values are an attempt to give a resistance number to components that react differently than a resistor. Condensors and coils are frequency dependent, so that makes it a LOT weirder.


Second question - I've seen the posts on metric - v - SAE fuses and thought many times about needing to get the right ones (which I haven't). So where does a person buy these metric fuses? If it's not a show bike, does it make sense just to swap in a different fuse holder? I can't seem to find anything other than regular buss fuses...[/quote]

Yes they are "metric" fuses, they're harder to find, more expensive.
After you've blown 6 or 8 in a trouble-shooting session, you're ready for a change.
So go to the auto part store and buy an auto-type fuse holder, or better yet one of those small circuit-breaker things. Cut out your old fuse holder and spice the new one in, you'll be a Happy Boy.
There's a photo of what I did here, somewhere on the "Recent 450 Project - Start" page.
http://home.comcast.net/~tbpmusic6/450site.htm

Just took a couple of minutes, less than $10 total.

If there are ever doubts about your coils, just replace the darned things. They were never designed to last 40 years and there are economical replacements available.
 

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Sensei
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many people just swap in a modern "blade-type" fuse holder..... Multi SAE fuse holders are available at radio shack and most electrical supply houses (graingers)....
 

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66Sprint said:
First, to Donny...... Reading through "extra" parts/wiring would increase the resistance.
I was picturing a situation where the coil could be measured on the bench (not connected to anything) with an ohmeter connected to two terminals of the coil, and that would produce a resistance reading. Leaving the coil connected to the ignition system and connecting the ohmeter leads to the same point on the coils as they would be on the bench, the ohmeter will read the resistance of the coil but there may be other paths for the current to flow from the positive lead of the ohmeter to the negative lead. Hence, the coil would be in parallel with something else in the ignition circuit, and the resistance reading would be close to the same or less than the reading produced on the bench.
 

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Gotcha Donnie..... And yes, you are correct if it's a more direct wire or connection of some sort (a parallel but shorter path would read as less resistance)...However, with the stock wiring, (and assuming both points closed) the only "duplicate" (parallel) path would be through the other coil, its point, through the plate, the point set for the coil you are checking, and the wiring back to your current "touch" point for the meter....BUT, with either set of points open, this would include the wiring to/through the condensors, and their effect would have to be taken into account as well...and at this point, the math diverges radically from what one would logicly expect.....
I should have said 'extra' wiring and/or components Generally/Usually would be indicated as increased resistance...... :D :? ;)
 

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Discussion Starter #12
One of the nicest things about owning old motorcycles is the opportunity I get every single day to be reminded how little I know. About anything.
 
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