WTB SOHC CB750 field coil

irk miller

irk miller

You've been mostly-dead all day.
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Looking for a good CB750 SOHC field coil. Needs to read 7.0 - 7.2 ohms and show no continuity between leads.
I've now bought two supposedly good ones from eBay sellers that turned out to be 8 ohms and showed continuity which is a defective unit. I'd be really grateful if someone here has one to sell and can show me some luck on a charging system that has not had good luck to this point.

Thanks, y'all.
 
Finnigan said:
Hm, mine has 7.5
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That might mean it's on it's way out. When it gets up to 8, that means it's open. When you put hook it to 12v, it should hold a sizable wrench to the side cover. The one in my bike is 7.9 and somewhat charges, but it won't even hold an 8mm wrench up. It'll maintain above 12v, but no longer gets me above 13v. Spark has gone weak over distance and it's begun fouling plugs as a result. Rick's Motorsports rebuilds them for $145, so that may end up being the way I go if I can't find a good one.
 
Did you try to ground it into a full field charge? If you have a car battery you can run the charge into that just don't overheat the dang thing... for some reason er another this seemed to work for me and mine charged real good after and that CB is on the road 7 years now :o
 
Tune-A-Fish said:
Did you try to ground it into a full field charge? If you have a car battery you can run the charge into that just don't overheat the dang thing... for some reason er another this seemed to work for me and mine charged real good after and that CB is on the road 7 years now :o
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I did it with the motorcycle battery, but not a car battery. If this will make a difference, I can try this this afternoon. The part that makes me think it won't work though, is the fact that it shows continuity between leads. Unless I understand it wrong, it shouldn't show continuity and this suggests the insulation has broken down.
 
deviant said:
I did it with the motorcycle battery, but not a car battery. If this will make a difference, I can try this this afternoon. The part that makes me think it won't work though, is the fact that it shows continuity between leads. Unless I understand it wrong, it shouldn't show continuity and this suggests the insulation has broken down.
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I don't remember checking for continuity before or after, just it was a weak charge and I had good results before with full field pulsing the dang things to get em up to mag strength
 
We talking about the white and green wires? There definitely needs to be continuity between those two.
 
Yep I think so Sparky... it's like recharging a magneto kinda sorta ??? Worked for me and used to have an orange tool to do this on ford alternators... jumps F+ to F- and bumps polarity like bipolar meds haha!

ubbthreads.php
 
When the field coil is installed, there should be no continuity between either of those wires and ground, however.
 
Sonreir said:
When the field coil is installed, there should be no continuity between either of those wires and ground, however.
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Here's what's going on: Green is attached to - bus. White is attached to + bus. While both wires are hooked up, continuity occurs between + and - bus. No continuity occurs when both wires are disconnected from the busses and continuity is checked with either wire. Field coil resistance is 7.9ohms. I have a reg/rec with no white wire, which is why I have it set up that way, so field coil is always charged. Magnetic field is very low. Not even enough to hold a 6mm wrench to the cover.
 
We might be using different terminology or I'm possibly misunderstand the test process you're using.

If the field coil had no continuity, you'd not be able to get a resistance reading across it. It would show as infinite resistance.

What kind of reading do you get if you measure DC voltage between the green wire (disconnected from the bus) and the bus?
 
Sonreir said:
If the field coil had no continuity, you'd not be able to get a resistance reading across it. It would show as infinite resistance.

What kind of reading do you get if you measure DC voltage between the green wire (disconnected from the bus) and the bus?
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That's how I understand continuity and resistance, but I've been told that I'm supposed to get continuity. I'll check voltage and reply.
 
Sonreir said:
What kind of reading do you get if you measure DC voltage between the green wire (disconnected from the bus) and the bus?
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I'm getting battery voltage. Right now that's 12.65v (battery at rest). The charging system, at +1700 rpms is only maintaining 12.5v. At idle, it drops below.
 
Resistance readings between all three yellows?
Any of the yellows have continuity to ground?
 
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