Topic: 1975 Honda CB400 Four Project - Rookie

[MoMo]

Rick,  it does seem as though 1 is not firing, and the others are rich-but that doesn't mean much at this stage. Is the end of the plug wire in good condition-you could be seeing spark but not adequate enough to fire. Also, the cap could be arcing to the head-crank it over in the dark to check for that.  The test for the rectifier is in the shop manual and I believe that is available here for download.  Look forward to seeing the pics and keep at it-you will persevere...Larry

[RickB]

Larry,

Thanks mate. Yeah I got that shop manual PDF for the stator issues so that's first on the list tomorrow. I'll try the crank in the dark trick too.

So glad my image hosting is back up and running, I live and die by this thread!

Rick.

[ivanhoew]

rick i cant remember if yuor using the stock coils ?if so sometimes water gets into the base of where the ht lead goes in and it all gets green and manky in there .then when the plug is in the cylinder ,and the spark is trying to fire against the compression pressure , instead it jumps to earth through the green manky bit on the coil .

the thing i did was pull the ht lead out of the coil , its quite tight,and clean in the hole ,then put in a new copper ht lead and a ngk plug cap .

also , if you have a ngk plug cap with ,say, 5k resistance built in ,and a resistive ht lead ,and a resistor plug ,it may simply be too much resistance .


regards
robert

[RickB]

Robert,

Nah I've got a brand Dyna S ignition with new plugs and new leads. I've double checked the gaps on the plugs too. The head is essentially brand new and as clean as a whistle, so no gunk.

The resistance thing though, that could have merit. How would I know if I have all those things you mentioned? I assume it'll be labeled somewhere? Wouldn't surprise me. The spark on the plugs isn't what I would call a fat white spark. More a a purple kind of one but I don't know what it's suppose to look like, it's taken me two years to get to this!

Rick.

[ivanhoew]

stick your meter onto ohms (resistance) ,and put it in the cap where the plug goes ,and the other end that goes into the coil .see what you get .

[fastbroshi]

   Good job on the stator test, that output looks good.  So you can check that off as functional.  Good for you to know for the future.
    I checked back a couple pages to see why you thought there was a charging system issue, and it seems you thought the state of the battery's charge might be causing an ignition problem.  If the charging system were subpar a cylinder not firing wouldn't be a symptom.    I'd still test the rectifier just so I'd know where it stands, if it were me.

[Doctorlumen]

+1 on the cylinder not firing due to the charging system fault. That sounds like a coil issue. A purple spark is most certainly not hot enough to do the trick in this case. Maybe double check that the wires that go to the coils (black, blue and yellow I think) are in good shape and are going to the correct coil. Also, double check all your carb settings (i.e: the air screws are all about two turns out). Also check the high tension leads to the plugs and make sure everything is snug.

You re-taped your wiring harness, didn't you? Its real possible something like a common black wire got fuggered somewhere. Don't be afraid to "tone out" the whole harness...it will totally suck, but it will insure the wiring harness' integrity.
Good luck, Man!

[RickB]

Thanks for the tips guys. My charging issue prevents me from riding the bike! I just wondered if it may have been restricting the amount of power that the coils are able to draw and thus affecting the spark. But as you've both said, it doesn't work like that. Thanks for the explanation.

I did notice today it idled a little bit better with the choke on a bit. So maybe it is my idle screws that just need adjusting? I will go over all the spark leads and double check the connections. I really need to sort out this charging issue first though before I start this fight.

I did re-tape my harness Doctorlumen. My mechanic had the bike running great not more than 4 days ago so before I rip into the wiring harness again, I'm going to explore my other options!

Thanks again guys.

[RickB]

Thanks for all the help everyone! I spent some more time testing this morning. Going over everything. Here it is in question and answer format so I don't get lost (and other people may benefit from it later on). This duscussion is primarily going on over in my CB400F Charging Issue thread but again, I've posted it here to keep this project area thread up to date.

Unplug both the alternator and the rectifier from the bike's wiring harness. Also disconnect the green wire from the regulator. Using your multimeter, check the resistance between the green
wire in each of those couplers, on the harness side of the coupler, to chassis ground. Do the same for the regulator's green wire. There should be close to zero resistance - like less than 1/2 ohm.

The green wire on the harness side of the rectifier to ground tested 1.5, the regulator green wire tested 1.7. Is this bad? Here's a photo so you can verify that I have the tester on the correct setting,



Plug the alternator back in, and reconnect the green wire at the regulator. Make sure the battery has a good charge. You're going to check stator output on the three yellow wires at the harness side of the rectifier coupler. Set your meter to read AC volts. Start the engine, and let it idle while you attach one probe of your meter to ground, and the other to one of the three yellow leads. Watch the meter as you rev the engine to at least 4,000 rpm. Then repeat on the other two yellow wires. What was the maximum AC voltage you saw displayed?

Maximums:
1: 20
2: 21.4
3: 21.7

Next test would be to disconnect the white and black wires from the regulator, jumper them together, and repeat the test. This will "full field" the alternator and force it to put out it's maximum when you rev the motor to around 4,000 rpm.

Maximums:
1: 19
2: 19
3: 19

60VAC if you tested between pairs of yellow wires rather than yellow to ground.

I did get up around 60 on all three.

Questions - With the key on, is the voltage on the black wire = battery voltage?

Black wire= 11.5 volts
Battery = 11.5 volts

Are you certain the blue jumper wire is making good contact with both wires?

Yep, I am.



Did you test resistance between each yellow wire and ground? There should be no continuity. The meter should read the same as if the probes weren't touching any wires.

Yes, it just read 1, which is what it says when nothing is connected to it.

Now for the rectifier. I followed the SOHC/4 FAQ guide (checklist shown below) in both the resistance and continuity settings as I wasn't sure which was correct.

Here is the results on the resistance setting:







Note the 1. I will refer to this as ERROR so as not to confuse myself.

VI.   Check the five leads on the rectifier.
A.   To perform a forward bias test first connect the red tester lead to the green ground lead.
B.   With the black tester lead test all three yellow wires.
C.   Resistance must fall between 5 and 40 ohms.

This showed ERROR, like nothing was connected to the tester for all three wires. See above photo to verify I have the tester set correctly.

D.   To perform a reverse bias test connect the black tester lead to the green ground lead.
E.   With the red tester lead test all three yellow wire.
F.   Resistance must be greater than 2000 ohms.

Same as above, ERROR for all three.

G.   Connect the black tester wire to the red and white rectifier lead.
H.   With the red test lead test all three yellow wires.
I.   All three must have between 5 and 40 ohms.

I got 2.4 on the left terminal then ERROR on the middle and right terminals.

J.   Connect the red test wire to the red and white rectifier lead.
K.   Test all three yellow wires with the black tester lead.
L.   Resistance must be greater than 2000 ohms. 

I got 3.5 on the left terminal then ERROR on the middle and right terminals.

Here is the results on the continuity setting:



VI.   Check the five leads on the rectifier.
A.   To perform a forward bias test first connect the red tester lead to the green ground lead.
B.   With the black tester lead test all three yellow wires.
C.   Resistance must fall between 5 and 40 ohms.

Left terminal: .530
Middle terminal: .578
Right terminal: .543

D.   To perform a reverse bias test connect the black tester lead to the green ground lead.
E.   With the red tester lead test all three yellow wire.
F.   Resistance must be greater than 2000 ohms.

ERROR for all three.

G.   Connect the black tester wire to the red and white rectifier lead.
H.   With the red test lead test all three yellow wires.
I.   All three must have between 5 and 40 ohms.

Left terminal: .001
Middle terminal: .551
Right terminal: .565

J.   Connect the red test wire to the red and white rectifier lead.
K.   Test all three yellow wires with the black tester lead.
L.   Resistance must be greater than 2000 ohms. 

Left terminal: .001
Middle terminal: ERROR
Right terminal: ERROR

Now for TwoTired's suggestions:





You DO want to know what voltage appears on the Black wire to the Vreg and how it relates to the actual battery voltage. Make two tests; at the battery terminals and the black and green at the Vreg and subtract one for the other.

Key in off position:
Voltage at battery terminals: 12
Voltage at black and green on harness side side at regulator: 0
Subtract one from the other: 0

Key in on position:
Voltage at battery terminals: 11.5
Voltage at black and green on harness side side at regulator: 11.5
Subtract one from the other: 0

Alternately, place one voltmeter probe on Battery POS and the other on the Black Vreg terminal. Then, place one voltmeter probe on the battery NEG terminal and the other on the Vreg Green terminal. Add these two readings.

Battery POS and on black at harness side side at regulator: 12.1 (with key in the on position, 11.9)
Battery NEG and on green at harness side side at regulator: 0 (with key in the on position, 0)

You mentioned you have a Dyna -S ignition.  Do you also have 3 ohm coils?  Can you measure the primary resistance of the coils?

I do have a Dyna S ignition but I got the 5ohm coils as I had heard the 3ohms might be a problem on my charging system. My headlight is off unless I turn it on as per the Australian model spec (I believe the US model was always on). I would like to measure the measure the primary resistance of the coils. How do I do that?

Maybe you should tell us more detail about ALL the electrical mods you've made to the bike?

There's the two relays, the lighting in the mini gauges, the CB350F right hand switch and the Dyna ignition with 5ohm coils. Nothing else has been touched and is as stock.

Thanks again for persevering through this for me. I owe you all a beer if this bike runs!

Rick.

[fastbroshi]

It looks like your rectifier may be toast.  It should only be giving 1/Error = infinite resistance on those reverse bias tests, since diodes only allow current to flow one way.  I'm sure TwoTired can confirm.

[CB400fss]

Hi , Been reading the thread today and I saw talk of sealed Batteries, I can confirm you can get the exact one to suit the CB400F, I have one in mine, but they are not all that cheap , they are well worth it as well, If you have a dodgy regulator I do have a spare, But you can also use a Bosch RE55 to suit a car alternator they work exactly the same way, just be sure to earth the case to ground, rs components have 3 phase rectifiers available and will need a heat sink when used, I also have bits and pieces for these bikes as I have 2 complete bikes and a wreck, complete ones are 75 and 76 both running with the 75 still in daily use

Replico in South Australia has replica side covers and if you have a sample he may be able to make a headlamp shell, There is another guy in South Africa who makes some really trick parts ( ttr400-com/ ) he sells in us bux, but is happy to send to AUS, I got an adapter from him so I could use an oil cooler on my 400/4, was excellent work and great value

[RickB]

G'day,

So the charging issue has been resolved. Thanks to everyone for you help on this. I couldn't have done it without you.

It was the rectifier. I replaced it with a used part that bench tested as working. Put it on, started up the bike and had 15+ volts at the battery straight away. Now I'm just trying to dial back the voltage regulator to meet the min/max voltages given in the manual.

Trouble is the bike is not idling at all. Lots of popping and farting and sometimes running on 3 cylinders, sometimes just 2. I'm getting a weak purple spark from the Dyna ignition. I tested the coils for resistance as per the Dyna specs. All good. I don't think it's getting enough voltage. I'm going through the wiring hardness polishing terminals, but apart from that I'm just trying to read everything I can on why I might be getting a weak spark.

All the plugs fire when outside resting against the casing. Just a faint purple spark, sometimes a white spark, sometimes an uneven spark. The 1 and 4 pipes were cold last time I tried starting it. So that left side coil pack. All the leads at the coils are good, double checked them. Haven't checked the resistance of the leads, not sure what they should be? The spark plugs, leads and caps are all brand new. I've got 9 new spark plugs, and swapping the guilty plugs for new ones doesn't fix the problem. Argh, more problems!

Anyone know some good threads on weak spark issue with Dyna ignitions? I have the Dyna S electronic ignition with 5ohm coils as per Dyna's recommendation.

Ok so some other bits I've been working because I was sick of looking at my multimeter.







Bending up a bracket for my seat. I want the seat to be easily removable and preferably with no modification to the frame to install.





Used some heat shrink to keep it from scratching the frame more than I already have. I'll probably swap these nuts out for something more user friendly. I'd prefer to keep all the hardware metric too, these are 1/4.



Some mud guard washers and low profile bolts should help spread the load and stop the fibreglass from cracking. Obviously there will be foam and upholstery covering them. The brackets aren't meant to be lined up. I have to correct for some un-eveness in the fibreglass work.



Holding it to the frame.





Not the cleanest fabrication work but when you're using an $11 hack saw, some scrap aluminium and a vise that is rickety, you do your best. It's all hidden anyway.



Drilling into the nice paint and fiberglass was scary. It did chip away a little, but it's hidden under a washer and the seat foam.



You can see the colour doesn't match perfectly under artificial light, but I can deal with it. It actually is way more pronounced in these photos than I've noticed before.



Lot's of finger prints, but you can how it sits. now I have to fix it to the frame some how at the front because the rear plate will crack the fibreglass is that's the only way it's fixed. I might have to drill a hole in the frame at the front but I'd like to avoid that. Any ideas?

All these cosmetic stuff can really wait, I need to sort out the spark issue ASAP. That's the only thing stopping me riding this thing!

Rick.

P.S. Larry, I haven't forgot to get you those shots of the exhaust. I'll do it tomorrow for you.

[MoMo]

Thanks, Rick.  Starting to take shape.  Hope you can track down the ignition problems-that is one reason I prefer points as the system is a heckuva lot easier to troubleshoot.  I just picked up a 74 CB750 with a Dyna S, if it develops any problems I will switch back to points. Glad you finally solved the charging issue-I'd say the rectifier in over 75% of the charging issues I have worked on is the culprit...Larry

[fastbroshi]

Good to hear you got the charging issue sorted.  This dyna kit you have, it's brand new?  I'm unfamliar with them personally so I might not be of much use there.   With the intermittence you described, it definitely sounds like something electrical and not fuel related. 

[Doctorlumen]

Wow...look at me being chatty. I posted up on your misfiring thread in the "Bikes" forum, also. But wanted to throw this out...have you tried swapping your dyna out for points to see if the issue resolves? Maybe ask your mechanic if he kept the points plate and have him swap it out and time it. If the points work, then job done there is your problem. Call up Dyna and see if you can get a new one.

[RickB]

Thanks guys.

Yep, I suspect electronics just because I've checked everything else!

I do have the old points plate, but I very much doubt the condensers are good. It looked very raggedy when I pulled it out. I'll get stuck into it some more tonight and see. I'm going to attempt a voltage test on the Dyna S ignition and then inspect all the the terminals supplying power to the coils to check for corrosion etc. If anyone has a list of terminals/couplings I should be checking, that would be fantastic. I don't really know how to read the wiring diagram well enough to see what is in the line to the coils.

Thanks again for the encouragement guys,
Rick.

[Spades]

Wow. I read page one and page 16 .. being new to the forum and having just recently gotten my SOHC, all I can say is I am stunned. That thing is amazing esp considering where it came from. That's just amazing.

[Anti-Johnny]

Wow. I read page one and page 16 .. being new to the forum and having just recently gotten my SOHC, all I can say is I am stunned. That thing is amazing esp considering where it came from. That's just amazing.

true that. I've been looking around for a 350 or 400 to have as around town bike after seeing what hes done here.

[GK]

good work Rick, just a couple of tips for you if you are looking for a cheap sealed battery here in oz you cant go wrong with www.allpurposebatteries.com.au  they are super cheap on the gel batteries I use them for my dragbikes.
also next time you are about to drill on glass or paintwork a good tip is to put masking tape down and then mark where you are going to drill and proceed no chipping or drill bit skating when this is done.
Ok I had better get my little 400 out from under the bike cover and get it finished seeing as we started our threads about the same time ouch!
cheers, GK.

[RickB]

Hi guys,

Thanks for the supportive words lads!

So today was an interesting day. With the help of my weak spark thread I was able to solve this (I hope).

So I did the voltage tests Dyna give in their support documentation that come with the ignition, everything checked out. I polished/cleaned the couplers at the solenoid, the solenoid/harness and key switch. I then took the leads off and measured them for resistance...

Spark plug lead resistance with tester on 20k ohm setting:

#1: 6.95
#2: 5.89
#3: 5.62
#4: 6.79

I immediately thought this was odd, given that I'm having trouble with the 1 and 4 cylinders. I then checked the length. Yep, 1 and 4 leads were a good 3 inches longer than 2 and 3. So I cut them all down to the same length (about 25cm/11inches). This was the shortest I could safely go with number 4, so I decided to make them all the same length.

I then checked for resistance again. They were all around 5.30 ohm +/- .20 or so.

I reinstalled them, started the bike and wouldn't ya' know it, it ran like a dream. Thick spark and firing on all cylinders!

I would never have though cutting my leads down by 4 inches would make such a difference. Anyway, it is chalk and cheese now. I even went for my first ride!

I made it half way home and then a fuse blew. I had to push the bike 2km home in the dark. The lower 15A fuse now blows as soon as I turn the key. No power, no lights, nothing. No idea what has changed, I was just riding along then it cut out. Maybe something shook loose and shorted?

Anyone know what circuit that lower 15A fuse is on? That should help me troubleshoot. Could it be the battery is overcharging from incorrect adjustment of the voltage regulator?

So I'm, on the hunt for more electrical gremlins but feeling very positive.

Thanks again for all the help guys,
Rick

[Doctorlumen]

Jesus, man. No rest for the weary.

[ivanhoew]

hoooray .nice one rick .

[strynboen]

get on the road..vith kamara glued on helmet..and drive the hell aut of it...cant wait anymore.....

[BenFrank]

First Ride is a wonderful thing isn't it?

Good on ya brother, keep up the good work and don't loose faith.

My '76 CB400F goes in Wednesday for an overhaul from a guy in my area who's known as a Vintage bike doctor... he works for fun and charges a pittance for an hourly wage! So excited to have someone who grew up with these bikes look for things I couldn't see.

You'll love your 400FOUR it's such a light fun little bike to throw around.

[RickB]

Hi guys,

Sorry for the lack of updates. I've been traveling. Mexico surfing and now Los Angeles for a while. I've had to leave the bike at home in the shed which is truly heart breaking.

I fixed the fuse blowing issue. It was an unshielded section of wire from the neutral light switch down near the starter motor. I didn't find it until I'd checked the ignition and both switches, but once I'd covered the exposed wiring with some heat shrink, I was good to go.



So the first real ride...







Obviously for a guy that's 6'2" a CB400F is a bit small. It doesn't feel as cramped as it looks. I was actually quite comfortable.









When I got home 5 hours later I had oil all over my right boot from a leaky clutch cable cover (the little triangle cover plate, not the big clutch housing cover) and my muffler was ruined.

The battery overflow fluid had sprayed up in the wind and onto the chrome of the muffler and stained it. The battery still had plenty of fluid and charge in it, but obviously it's overcharging. I think I need to tune down my voltage regulator. The muffler is a shame, but it was only $59 so I'll get another one.

Rick.