Honda-SOHC
SOHC.co.uk Forums => CB350/400 => Topic started by: exvalvesetdabbler on August 04, 2026, 07:47:35 PM
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Trying to expel an electrical gremlin. Up until last week I hadn't been out in the dark for over 30 years. After 20 minutes with the headlight on battery voltage had been pulled down to 12v that was cruzing on A road with about 5000 rpm. Day time riding no issues
Currently going through all the connections and testing reg and rect on the bench.
Currently trying to track down where the loom gets it ground connection from. I have found 2 so far, one underneath the tool tray and the brass strip on the rectifier. Have I missed one or is that it?
I have ruled out the bonding on the headlight/indicator bracket and the rear lights since the green wire is providing ground to parts that are rubber mounted.
Traced all the wiring associated with the alternator, rectifier and regulator.
Yellow wires from rectifier to alternator resistance within spec between each wire about 0.6 ohm
White wire from regulator to field coil 5 ohm
Red/white from rectifier back to starter solenoid battery side ok
Forward voltage drop and reverse leakage of the diodes in the rectifier
I'm going to substitute another regulator as soon as I have time. Bench testing it, the transition between mode 1 and 2 happens 13.8/13.9v. mode 3 at 15v
What I have noticed is the suspect regulator hangs when going from mode 2 back to mode 1 at about 12.3v. mode 1 to 2 at 13.4v.
Can't see why it might do that other than grubby contacts, cleaned them already.
Black wire for the regulator traces back to other black wires ok.
Accuracy for resistance / continuity corrected for meter lead resistance.
Although it didn't seem necessary I have since checked and cleaned the connectors involved just for fun.
What have I missed?
Regards
Dave
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Not done a 400 for a long while but most looms of that era had the main earth point near the coils. A big old round one which bolted to the frame, normally where the coils mount at the front. Bikes like the 500-4 had a specially made metal plate to aid the contact area. If that area has been painted or powder coated you’ll need to go back to bare metal to help it make contact. Same for the battery earth, bare metal next to the contact and the frame. People miss that all the time so if that’s the case you certainly ain’t on your own.
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Thanks, you may be right, I do remember there being an eyelet under the horn bracket. Never clocked that it might be a main ground point.
I'll check the voltage on the green wires against battery terminal when I fire it up tomorrow. With some current flowing there should be voltage across any grubby connection. At least the green on the reg needs proper grounding to get a valid reference. I know the rectifier is grounded, no resistance between green wire in the connector and frame with it unplugged.
The frame was painted in 1983, so possible a bit of corrosion may have got in. I would have used vaseline on them at the time based on what was on the bathroom shelf. Dad used it for something, I remember him squeeling like a stuck pig one night when mother left a tub of vapour rub next to it!
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Regulator numbers sound about right, you need to check battery voltage when running with both lights on and off, most common problem is corroded yellow wire connectors where stator connects to loom, you can also check the ac voltage accross each of the 3 pairs of yellow wires exiting the stator
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Battery voltage is 13-15 without headlight.
That's why I suspected one phase may be disconnected and the regulator was compensating up to a point. Measuring resistance between each of the yellow wires in the rectifier plug rules that out. Same for the field coil going from the regulator end of the white wire. My alternate theory was a bad earth on the reg or rect that was lifting the reference voltage of the ground locally with increased current of the headlight.
The rectifier is well bonded now, I cleaned the brass earthing strip and the contact point on the frame. It's grounded ok with the plug disconnected. It's a bit of an odd design that the regulator doesn't have bonding to the frame and relies on the harness only.
The only thing I am seeing is the regular hanging when it should be dropping back from mode 2 to 1. I have been bench testing it with an indicator bulb to simulate the field coil load.
The spare regulator that I have dug out has a tight mode 1-2 transition around 13.8 - 13.9 in both directions.
I'll have another poke around. I need to find the other earth point under the tank and check that first.
Regards
Dave
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I might be staying the obvious, have you checked the contacts in the regulator are not badly pitted.
I cleaned mine up then adjusted the contacts as per the Cycleserv manual.
I'll attach the relevant pages shortly.
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I think that's where we are going to end up. Hopefully swapping out the regulator once all other obvious options have been exhausted. If the replacement works I can then tear into the suspect one.
I had kept the spare to one side with the intention of adjusting the top limit to be compatible with an AGM battery without risking mucking up a working reg. And doing it at my leisure over winter.
Regards
Dave
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If there is an alternative to the shop manual for the adjustment, I would be greatful if you could share it.
Regards
Dave
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Any reason you don't like the Shop Manual explanation? seems pretty exhaustive and fairly understandable to me.
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Just like to be fully prepared and there is always more than one way to skin a cat. Pictures aren't that great where it mentions bending bits.
Looking at the actual mechanics, it looks like you loosen the top contact and slide it to get the right transition point. That also moves the bottom contact that you then need to bend to get the 15 volt limit.
Regards
Dave
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Been a while since I've adjusted a reg but I found it very easy. You do it and check where it kicks in and adjust accordingly is my recollection.
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Problem solved.
https://youtu.be/MS2DCoaTgyw?is=vlRNYS2l2ZjsI1_Q
Side note, if that voltmeter wasn't there I might have been pushing it home. I managed on pilot light the last few miles.
Swapped out the regulator and now getting 13.5 to 14.1 on a fast idle with the headlight on main beam. The old one would have been draining the battery at 5000 rpm.
I'll take it out tomorrow and wring it's neck on the dual carriageway and see what it tops out at.
I kind of had an idea that this is where the problem was but several minds are better than one desperate one. Thanks all.
Gives me a free hand to muck around with the old one knowing that I'm looking for a 13.9v transition between mode 1 and 2 during a static test on the bench.
Regards
Dave
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Hope this information helps.
(https://live.staticflickr.com/65535/55443627952_09d7aacb43_b.jpg) (https://flic.kr/p/2stn5XS)1 (https://flic.kr/p/2stn5XS) by Macabe Thiele (https://www.flickr.com/photos/187487200@N03/), on Flickr
(https://live.staticflickr.com/65535/55444593191_18fb7191b5_b.jpg) (https://flic.kr/p/2sts2TV)2 (https://flic.kr/p/2sts2TV) by Macabe Thiele (https://www.flickr.com/photos/187487200@N03/), on Flickr
(https://live.staticflickr.com/65535/55444989540_f2ff165209_b.jpg) (https://flic.kr/p/2stu4Hw)3 (https://flic.kr/p/2stu4Hw) by Macabe Thiele (https://www.flickr.com/photos/187487200@N03/), on Flickr
(https://live.staticflickr.com/65535/55444989540_f2ff165209_b.jpg) (https://flic.kr/p/2stu4Hw)3 (https://flic.kr/p/2stu4Hw) by Macabe Thiele (https://www.flickr.com/photos/187487200@N03/), on Flickr
(https://live.staticflickr.com/65535/55444989525_a2a315b351_b.jpg) (https://flic.kr/p/2stu4Hg)4 (https://flic.kr/p/2stu4Hg) by Macabe Thiele (https://www.flickr.com/photos/187487200@N03/), on Flickr
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Thanks. That looks like the shop manual. It's the bit they are bending I can't see clearly. The copy I have is probably worse though.
Regards
Dave
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Thanks. That looks like the shop manual. It's the bit they are bending I can't see clearly. The copy I have is probably worse though.
Regards
Dave
When you have the cover off it's more obvious what they mean by the adjusting arm.
The paragraphs 1 to 4 then make sense.
It's 4 years ago that I adjusted mine, I actually bought a used regulator that was no better, I ended up fitting the original unit after cleaning up the contacts with one of the wife's nail boards.
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The one that's working came off a bike with 72k recorded mileage, so we'll see how long it lasts.
The black cover was a bit crusty so might be original. Inside looks good as new.
Dave.
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Just curious - did you think about replacing the OEM rectifier and regulator with a solid-state "modern" component like the one DSS sells?
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Best thing for cleaning point, wherever fitted, is a thin flat diamond file, i have lost my 45 year old one!!
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Best thing for cleaning point, wherever fitted, is a thin flat diamond file, i have lost my 45 year old one!!
Wendy would not lend me her diamond dust nail file. ☹️
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Just curious - did you think about replacing the OEM rectifier and regulator with a solid-state "modern" component like the one DSS sells?
The standard set up is normally reliable, well it lasted 49 years. The only advantage would be if the maximum output was more in line with battery manufacturers guidelines for sla or AGM batteries.
Regards
Dave
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Just curious - did you think about replacing the OEM rectifier and regulator with a solid-state "modern" component like the one DSS sells?
I considered that option, not sure how comprehensive the wiring guide is that presumably comes with the kit.
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Just curious - did you think about replacing the OEM rectifier and regulator with a solid-state "modern" component like the one DSS sells?
If you're thinking of this make sure it's one that uses Mosfets, I think the Electrex one does but ask first before buying.
https://www.electrexworld.co.uk/cgi-bin/sh000001.pl?WD=cb550f&PN=RR24%2Ehtml#SID=439
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That's the same unit DSS sells - though both Electrex and DSS are out of stock on them at the moment.
I had thought about replacing my rectifier/regulator with one of these back when I first bought my 400F several years ago but since the OEM units were working fine (and still are) I decided to wait until they quit! :)
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I fitted one of the new DSS combined units 10 years ago after a charging fault, just about limped home, thank Gawd for the kickstart!! I am not an electrician, especially when it comes to charging/rectifier systems. After making a mounting plate from an old brass window hinge, (yes, really!), the new 'potted' unit was fitted where the old regulator was sited under the left side=cover. There was just enough slack in the wiring to the old rectifier to reach across to the left side. So far, so good.
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Here's what I found after trying to clean up the contacts.
[attachimg=1]
[attachimg=2]
Not sure if this can be saved
The bottom contact cleaned up ok
Regards
Dave
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Need a clean with a diamond file
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I have tried making adjustments to the failed regulator after having cleaned the contacts. Charging with the headlight on is happening right down to 2500 rpm, below that the battery is just about breaking even. This is done by bending a tab that preloads the strip of spring steel on the armature as per the shop manual.
With both the replacement and the refurbed regulator I'm still seeing 15.6v without the headlight on if I ride it like I stole it so a little fine adjustment for mode3 is needed. Where that happens turning the headlight on drops it to 14.4-14.6 so I can manage that for now. Probably no bad thing having the headlight on when tearing around like a scolded cat.
Setting mode 1-2 transition on a bench power supply with a lamp in place of the field coil is straight forward.
Setting mode 2-3 transition is a little more tricky. With the power supply current limited just below the current drawn when it's hard into mode 3, provides some simulation of the interaction between field coil excitation and voltage that gets the contacts vibrating but the observed transition is about 0.6v lower that what it produces in the bike.
Armed with that data I'm fairly sure I can reduce the max voltage to acceptable limits. I haven't played with this adjustment yet.
As a parallel issue I have been looking at how these combined units work without the benefit of a big ballast resistor to switch in/out as needed. It seems a good proportion of these devices achieve regulation by pulsing a short circuit across the stator. Obviously MOSFET transistors are better in this scenario than bipolar transistors because of the lower on resistance and negligible heating, it does mean that your alternator is running at max output regardless of how much power is used and how much is dumped at source.
Does any one have any solid info on any combined units that actually modulate the supply to the field coil the same as the OEM reg.
All of the sales patter I have read doesn't really go into operation of the device.
Regards
Dave
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Try an email to Electrex. They seem to be ok on answering questions.
15.6v seems excessive. Battery boiling time :) :)
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Yes and even worse if I want to keep it down further for AGM.
It probably won't boil at that but will need frequent deionised water top ups
Thing is without real time voltage readings you probably wouldn't know as I didn't coming home after dark and seeing the battery voltage creeping down below 12.5.
For now I'm getting solid 13.5 -14.5 over a range of conditions which is better than what I had before, draining the battery with the headlight on.
I didn't see this coming since I was getting 15 going down the open road without headlight but looking at the voltages, it probably wasn't putting much back into the battery pottering around town. Goes a long way to explain why a 3 year old battery is struggling to turn the engine over. I kept it on an optimate over winter but didn't bother much over summer where it was used regularly.
Regards
Dave
Regards
Dave.
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I managed to install a digital volt meter inside my tacho. I was also concerned about battery drainage and over volting etc and wanted to keep an eye on it without having a eyesore of a gauge or meter stuck somewhere. Saw something on Alan Millyards 6 cylinder Z1 and thought it was a great idea, as I had the tacho apart for renovation I thought I’d try and fit it in there instead. Waterproof and highly visible. Had a choice of colours as well, still undecided on which one I’ll go for, blue is too bright, red is right in your face, green looked ok as did amber. Might put a small resistor in the lighting wire to see if I can mute the brightness a little.
I posted a pic of it a couple of years ago and go slated for doing it by those who think it’s not needed. I ignore them, it’s my bike I’ll do what I want. If I end up not liking it I’ve got a spare tacho already renovated to fit in its place. 550f2 clock btw. Not sure there enough space inside a 400 or 500 clock.
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Ken, for daylight visibility blue is the way to go together with some blue or grey perspex as a contrast filter.
I have the same unit that you used, I ordered blue and they sent me orange, impossible to see going down the road. I guess red would be similar.
The blue one that I have now is easy to see and those units can be adjusted to account for the small voltage drop between the connectors in the headlight shell and the battery. Ideally you need a small relay and dedicated fused wire from the battery for monitoring.
They come in two variants , single wire that just measure what it's given as power and the two wire version that has the measuring wire seperately to power. Seperate measuring wire means v low current and no voltage drop on that wire. It's easy to convert from one to the other if you have a steady hand and soldering iron.
I had planned to wire mine up with a separate monitoring wire eventually, but at the moment it's doing its job. Just need to calibrate my brain to add 0.3v to the reading for now.
Should add that the contrast filter makes all the difference. Loads of suppliers on fleabay who will send you a 'sample' of 3mm perspex quite cheaply.
Regards
Dave
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I have loads of perspex lying around. Mine has 3 wires. I was intending to just wire ot into the black power feed of a Honda. Only want it displaying when the ignition is on. I blew one up accidentally, I bet I blew the blue one 😋😋😋
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If you wire it up from the headlight shell, you get a small voltage drop as I would expect when the coils are energised. I set mine up to read right with the kill switch set to off, so very little current flowing in the switched live. Easy to check battery before firing up.
Wiring measurement wire back to the battery and a relay off the ignition wire is best if you have time and patience.
Regards
Dave
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So long as it gives me some indication of a fault occurring that should do. If I see it dropping I can always head home turning stuff off as and when it becomes advisable.
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That was my thinking at the time and it has saved me a walk home.