Topic: 1972 CB350F new coils, which post gets the black wire?

[jrmull]

Hi,

I just got new coils on ebay that have two posts but they don't say + or - next to them.  Does it matter which post gets the black wire and the other is either get the blue/yellow from the points?

Normally, I would put the black wire to the + indicating switchable battery line.   I think it doesn't matter.  What do you think?  Thanks.

[jrmull]

Problem solved.

I looked a little harder at each coil and there is a + and a - sign marking.  A hard to see, but there.

So the + is my black wire from the battery when the key is one.   The other post is negative - marking from the points.  1-4 is blue wire coil and 2-3 is the yellow wire coil as the negatives.

I was reading various suggestions and some saying, makes no difference and others saying it does matter.  Since it is marked, I will match the positive/negative setup.
 

[bryanj]

What does matter more is that the ohm reading on the new ones is the same as the old ones, dont believe vendors who say will fit

[Deltarider]

Also not unimportant is that the + is connected to the B/W and not just any black wire.

[PeWe]

+3, Kill switch need to work too!

My Dynatek coils have no markings for + and -
Connect as you want. Plug wire direction most important.

[jrmull]

I got this from ebay.  It had the + - on the side posts.  Really looked great, right size, good wires.....excited.  Until...

[jrmull]

Until I discovered the mounting holes are on the side not top.  The mounting spacer brackets wouldn't work unless I drilled out the coil which is not practical.

[jrmull]

Of course the solution is to drill new holes in the frame and use bolt nuts to use as spacers.  Been there done that with some Taiwan coils 9 months ago that (my error) I left the ignition on too long and fried one.  That one, I had to drill to fit also.  Anyway, if you buy this current one, wires nice, wrong for a 1972 CB350F

[jrmull]

So wired up and satisfied it is well grounded to the frame.....but I have a voltage difference from battery to the coils.  I have 12.80 at the battery and with ignition on, the coils have 11.80. 

I lose a volt.  Is this normal for a 1972 CB350F ?  That much loss from battery direct to coil since it goes through a single fuse, then harness, then points, condenser area, up to the coil input? 

I charged up my MottBat (good one 9 months ago) and it was 13.80 when done, but the coils are showing 12.80.  Still a volt less.

It looks doable but I guess the answer is to back track from coil to the points, etc to find the voltage loss.  Curious what you guys have.  Thanks

[bryanj]

Ignition switch can be a bad contact  and cause volt drop. You need to check volts at each point along to find where the drop is

[Deltarider]

That voltage drop is not dramatic when the engine is not running. After all, you have consumers switched on. Do the same test again with the engine running let us say @ 3000 RPM. I bet you the drop will be less.

[Bodi]

Coil power goes battery - fuse - keyswitch - killswitch - coil. Points are in the ground circuit.
Voltage drop depends on the harness circuit (between battery and coils) resistance and the circuit's current. Current at 12VDC varies with coil resistance. Do you have normal 5 Ohm coils, or are yours lower? The 350 will struggle to charge with lower resistance coils (and almost always fail).
It may be possible to have both coils powered at some crank position with points, but some aftermarket electronic ignitions definitely do this.
Running coil current is lower than stopped, because tha AC impedance of the coil is higher its than DC resistance (but not by a lot). If you do have both points sets closed for a static test, when running this is only for a fraction of a crank rotation.
Other than due to coil current difference when running vs static, harness voltage drop does not change for engine stopped vs running: it's solely a function of harness circuit resistance and current.
And one Volt is at the upper end of what I would th8nk OK. But not atypical. If a piece of harness gauge wire was connected from battery to coils, you would get somewhere around 0.1V voltage drop - assuming 8' of wire, gauge between 18 & 16AWG, and a single 4 Ohm coil load @12VDC.
You can't eliminate the wire. The rest of your drop is from the fuse, switches, and connectors... these can at least be cleaned to minimize resistance.

[jrmull]

Thanks Bodi for the good details.  My original coils are 8.4 and my new after market ones are 7.8 measuring the primary.  The secondary was 14.28 for the OEM and aftermarket 15.36.  I was measuring at the post the black positive wire going into the new aftermarket coils.  I didn't consider that the coils are actively loading up and consuming.  Thanks for that info.  The wires from the new aftermarket coils are thin 16ga and I will consider replacing them with 12 ga thicker wires.  Someone mentioned they had a diagram to direct wire from the battery to the coils with proper fuse and switchable protections.  I will post it when available.

I was headed this way because I was having random problems with spark.  So I am replacing with Dyna S ignition.  Reading details, I decide to replace perfectly good coils and perfectly good rectifier and regulator with digital rec/reg single combo.  I think the coils are ok but likely the biggest weakness being 40 yrs old.  The Dyna S instructions warned me about voltage needs, so checking is good instead of slopping the part in to see what works.

Again thanks for the details.  I will track the voltage backwards and see if there is something that stands out.  Regards John

[Deltarider]

May I suggest once more to do the test with a running engine like I proposed in reply #10? You can select the 2V range and measure the drop directly between the Batt POS terminal and Coil POS. BTW, I doubt Dyna is a good choice for your bike. My OEM coils are 45 years old and still good. As a matter of fact I consider reusing them again instead of the bulky 3Ω Dyna coils that are on it now hindering the clutch cable. In this forum there is lot of talk of feeding the coils directly by a relay. Personally I think that is exaggerating things, let beside the relay will cause some drop itself. But you can do a simple test to prove I'm wrong. Have the engine run say at 3000 rpm in standard configuration, then whilst it is running connect an extra wire from the Batt POS terminal to Coil POS and see if that increases the RPM. But even then: if there is a significant V drop, it needs to be adressed. The usual suspects are the fuse and fuseholder and the IGN key switch. Some V drop is normal however. The standard kettering ignition system is designed thus that there is enough margin to deal with various voltages. Just use the bike for what it was intended and avoid short rides.

[jrmull]

H DeltaRider.  My goal was to install a Dyna S ignition system and replace the points.  In the process, Dynatek installation comments did say 1 volt was normal at the coil, so others are saying similar.