Honda-SOHC
SOHC.co.uk Forums => CB350/400 => Topic started by: royhall on December 24, 2015, 08:17:09 AM
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Discovered yesterday that after the initial superb results with the 350F that I now have a 3.5 cylinder bike.
When I put the coils on (originals) I noticed that one HT lead was turning in the coil and was quite loose. But decided to go along with them anyway.
Not sure at this point if its on the bad running cylinder (Christmas duties prevent vital garage time, Bah Humbug) but from memory I think it may be.
Anyone else had this problem.
Cheers and Happy Christmas.
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It is very likely to be your problem. H.T. circuits don't like loose connections, they can make and break with the vibrations from the engine, or road bumps etc, at least it's an easy fix!
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If you replace the coil or coils take care that you get them with the same primary coil resistance.
The Honda coils on my CB350F had a primary resistance of 4 ohms but the replacements from David Silver only had a 2 ohm resistance which would have drawn far too much current through my Boyer ignition unit. I had to fit a pair of 1.6 ohm ballast resistors in series with the 12v supply.
(http://i41.photobucket.com/albums/e254/gtmdriver/DSC00012_zpsv6myfvuy.jpg) (http://s41.photobucket.com/user/gtmdriver/media/DSC00012_zpsv6myfvuy.jpg.html)
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VERY common problem with those coils and Cb twins coils. I am supposed to be writing up how to fix this step by step with pics. Will do it next week as I have two sets to do and I now have all of the materials . BUT I can't find a sourceof the thin rubber sleeving on the outside of the HT lead to make it look original.
Ash
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Hi Ash, try googling this stuff, it's not cheap, and it's branded, but that branding should be removable with MEK. It's about 1mm wall when heated and shrunk. Use the 12/6 size 12mm to 6mm. I've got it on some of the boats wiring in the engine room.
[attachimg=1]
It might not be of any use but it's a lead!
Regards
Nigel.
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Not checked the resistance on the original coils yet, but the pair of Silvers replacements read 3.4 and 3.1 ohms. I am assuming this will be okay as I am running points. Is this correct. Cheers.
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Not checked the resistance on the original coils yet, but the pair of Silvers replacements read 3.4 and 3.1 ohms. I am assuming this will be okay as I am running points. Is this correct. Cheers.
You should be OK with these. The points may burn a little quicker but you should be OK.
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Hi Roy. The various four-cylinder SOHC Honda manuals are scant on resistance details referring you to the Honda dedicated electrical tester. The '60's twins manuals were much better on this. Those coils sound Ok to me, I think the cold stall current of the coils should be 3-4 Amps so if you take 12 volts and Ohms low this equates to 12/4 -> 12/3 Ohms = 3-> 4 Ohms (R=V/I).
You have to be careful with cheopo multimeters as the low Ohms range is often not very accurate. The best way of measuring resistance with a cheopo one is to put a known resistor in series with the coil and measure the current through the coil and the voltage drop across the coil. The resistor wants to be about 15 Ohms. You then work out the resistance of the coil using Ohms law R=V/I . Doing it this way you are only passing a lowish current through the coil and minimizing the self-heating, as the coil resistance increases as it self heats. Obviously, if you have an expensive meter (Fluke or TTi) it's not necessary.
Attached is the type of info in the sixties Honda gave.
[attachimg=1]
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Thanks for that Ash. Cant say I understood it all though. ;D Take your point about the cheap multimeter. My garage one is a cheapo but I have a fluke on the work van (couldn't be arsed getting it out), so will test them again with that. Will be interesting to see if the readings are different. Will post the new readings later. Cheers.
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There's interesting, didn't expect them both to be the same. They are both 2.7 ohms on the Fluke, retested on the cheapo and got 3 & 3.3 this time. Think I will bin the cheapo, it was only £3.99p with 10 litres of BP. Does that change them being okay to use on points. Cheers.
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The lower the resistance the more current will flow through the points and the condenser so their working life will be affected but points are not so critical as electronic ignition.
My Boyer system, for example, specifies a minimum coil resistance of 4 ohms.
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Thanks for that Ash. Cant say I understood it all though. ;D Take your point about the cheap multimeter. My garage one is a cheapo but I have a fluke on the work van (couldn't be arsed getting it out), so will test them again with that. Will be interesting to see if the readings are different. Will post the new readings later. Cheers.
Roy ...if in doubt ask ..please don't say you don't understand ... I can always elaborate ;D ;D ;D
Just measured two CB750 coils TEC FL703-12V coils with a high accuracy bench DMM at work and one reads 4.60 Ohms and the other 4.65 Ohms .temperature 19°C.
Secondaries measured 14,540 and 14,930 Ohms ( 14.54k Ohms and 14.93k Ohms). if they read open circuit it is almost certainly the HT leads that have fatigued at the point they come out of the coil. If the reading is much higher you have a supressor cap with resistor fitted internally. Remove the cap and remeasure, in this case.
Brought all of my coils into work to do the fix on new HT leads ... so watch out on here later this week for details and pics.
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Not a problem Ash. I didn't know what ohms law was, its a long time since I last heard that in college. But thanks to the power of Google I am up to speed. Holding off on the job until your coil repair post appears. Cheers Ash.
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Out of interest what manufacturer code do 400/4 / 350/4 coils have on them?
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Will have a look when I get home.
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The code on the 350/4 coils is FL703-12V. Cheers.
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This is really a message for Roy. Had some fun and games and trashed a set of (faulty anyway) coils during the Ashimoto repair experiments. However, making good progress now with plan 'B' . Basically the TEC coils are encapsulated in black thermoplastic material. The secondary coil brass terminal inside can be got too quite easily BUT on one lead, if you try to de-solder the old HT lead from the terminal, the heat melts the plastic, the terminal comes loose,and the really fine wire from the secondary coil just snaps off and renders the coil useless. So I am just soldering onto the remains of the old lead.
Totally different with the Honda twins coils made by Nippon-Denso (yellowy/brown plastic body.). They are much easier to get to the internal secondary terminal because they are made from filled epoxy/ or thermoset resin which files/ grinds really easily. The HT lead conductor literally pushes into an internal pointed pin,no soldering. May solder it dunno yet. Was a bit worried that the replacement HT lead would not screw onto the metal -clad plug caps I just got from Germany but it's OK, after you create an initial hole where the conductor wire is, to start it off screwing in.
All 'TEC' coils (four Cyl) around bit less than 5 Ohms ... Nippon-Denso's (twins) 3.8 Ohms..
Still need to find rubber sleeve 1mm or less wall thickness. I don't want to use heatshrink, not flexible enough.
Progress and PICs to follow but on none of my coils, so far, is there any coil failure, just HT lead fatigue where the HT lead comes out of the coil.
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That's very interesting reading Ash.
As I have them do you think the DSS coils will be okay at 2.7 ohms with points, or are they going to eat the points and condensers?
Have been thinking of fitting a Boyer instead and have noticed they do a full kit including matched coils but it's really for a 400/4. If I go electronic that's the route I shall take.
Just weighing up before I fit the other coils, if I should return them to DSS and put the money towards the Boyer kit. I remember someone fitting the 400 kit to a 350 but can't find the thread now, some difference in the advance curve if I remember correctly.
What do you think Ash.
Cheers.
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I think these may be the threads you are thinking of Roy.
http://www.sohc.co.uk/index.php/topic,8952.msg61112.html#msg61112
http://www.sohc.co.uk/index.php/topic,9062.msg62181.html#msg62181
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Pretty sure the same setup on 350/4 as on 400/4 Roy. Makes sense to buy everything from Boyer although standard coils should be fine I think. Points with coils less resistance than standard sounds like bad news though as your points would arc and wear more with the extra current. DS pretty good on refunds & returns.
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Taken the plunge and ordered the full Boyer kit including the coils off eBay. Strangely I couldn't find it anywhere else.
Will update the 350 Project thread with the details when it arrives.
Thanks guys for the advice.
Will get an email off to DSS in the morning and get a refund on the pattern coils. Will let them know about the resistance issue at the same time.
Don't know if that will change anything as DSS are only a retailer for these, and they are available in many other places.
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If you buy the Boyer kit you will need their coils too as Boyer specify a minimum coil resistance of 4 ohms.
As I posted earlier you can use the DSS coils with the Boyer system but you need to wire a 1.6 ohm ballast resistor in series with the power (black) lead on each coil.
I posted a few photos about the Boyer system a couple of months ago so if you search under my user name you should find it.
http://www.sohc.co.uk/index.php/topic,8979.msg61594.html#msg61594
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Yeah found that post, very helpful. I have gone for the full boyer kit with coils as its really one of my existing coils thats failed. Thanks.
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The new Boyer Bransden kit arrived today. I'm now in need of a little more help.
The coils are not direct replacements, and I assume that although its a £220 kit you have to make all the brackets yourself. Also I've no intentions, after spending 100's of hours restoring a bike to as new, of tie wrapping a digital box to a frame tube. I will have to manufacture a more elegant solution than that. Were not off to a good start.
[attach=1]
Thought I would see what the resistance is across the Boyer coils, and its only 1.4 ohms. What the hell, now I'm confused, I thought it was supposed to be over 4. My existing coils are 5.1 ohms, whats that all about. I assume its to do with some digital wizardry, and the fact the coils are linked in series?
Also are these standard (new) plug caps okay for this application, says something about 5000 ohm suppressed?
Beginning to wish I had just bought one genuine replacement coil instead.
[attach=2]
Any ideas anyone, and does anybody have a photo of the best way to fit this kit to a 350/400 four.
Saves me reinventing the wheel. You may have guessed by now that electrics to me is all magic and conjuring.
Thanks.
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No.
The Boyer kit that comes with their own coils is different to the kit designed to use the OEM coils.
1.5 ohm is correct for that particular Boyer kit.
The lower resistance allows more current to flow to produce a fat spark but the Boyer kit you have bought is designed to handle that current.
As to mountings I can't help you there. I'm the person who inelegantly ty-wrapped the box to the frame.
Stick with it though. You'll be very pleased with the final result.
Have you tried contacting Boyer as regards the mountings? They are usually very helpful.
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Also are these standard (new) plug caps okay for this application, says something about 5000 ohm suppressed?
The NGK plug caps listed by DS are P/N VD05F (plugs 1 & 4) and XD05F (plugs 2 & 3).
The 05 in the P/N means the caps are 5K ohm resistance, the resistance being to do with suppression.
So yes, your plug caps should be OK.
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Thanks guys. Will make up some proper aluminium mounts for the coils and digi box. Will post what the outcome is in the project thread, with some pictures. Cheers.
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