78 KZ 650SR Igniton Coils:

Hey everyone, the more I looked and thought about this thing, it just didn't seem right. First of all my "digital" Volt/Ohm Meter was junk and my neighbors was wose than mine. I finally got an anolog VOM from another neighbor. I put a AA battery in it and it worked fine and gave reading on my coil right where they were to be. So, OK, why didn't the #3 and 4 plugs appear to not be firing? After soem on my knees study, I deduced that they were firing, they just weren't getting any fuel to fire !!!

I bought a set of 79 carbs on E-Bay a awhile back so I bolted them on and not it runs like I remember my new 78 and low mileage used 79 running. What a rush it was to take a ride with all 4 firing again.

This bike is titled a 78 but it has a lot of stuff that should be on a 79 model. It has the drilled brake rotors, auto adjusting cam chain tensioner, the accelerator pump on #2 carb and the 79 SR650 emblems on the side panels. It was built in October of 78.? Anyone have any light to shed on this? My new 78 was this color red but had different side emblems that said KZ650 and the SR was below that. The 79 I had was purple but had these style side emblems. They were both too new for me to do much work on them or get to know them mechanically.

Anyway, thanks to all of you who took the time to reply to my post, hope I can repay the favors some day.

Tom

It seems to me that bike models and years are like cars. You have a 78 built late in the year, but with 79 features. I have an 84 GPZ built early (Jan 2 or 3 if I remember right) that has features of an 83. Doesn't bug me since I figured it out. The big 3 do stupid stuff like that once in a while.

bountyhunter wrote:

Here is how it is shown to be connected in my FSM. As shown, the spark plugs split in parallel off the high voltage end of the secondary winding. Each spark plug branch has a separate path to ground.

What year manual do you have? Both my 79 KZ750 Factory Service Manual and my 80-82 KZ750 twin Factory Service Manual (along with the 650 and 1000 manuals) don't show it that way, and my 79 manual says it covers 76-79 models.

You do realize that if your drawing is correct, then the testing procedure also given in the manual is incorrect?

By the way, the coil in your drawing won't work anyway, it's wired wrong


Here is a pic of the page in the 76-79 KZ750 FSM



If anyone seriously believes that because the above pic shows a ground between the two plugs that the spark goes to both plugs at the same time, and then directly to ground, then I invite you to do a simple experiment (you do seriously believe you're right, correct?).

Pace a small piece of rubber under the kickstand to isolate the bike from ground, then remove two plug wires (on the 750 twin, or two wires on the same coil on a four) and hold one in each hand (being sure to touch the metal center), and have someone else turn the key on and hit the starter. Now, since you are electrically isolated from the bike ground, if you are correct then you will feel nothing as the motor spins over. So if you are 100% certain that I'm wrong and you're right, give it a try.

Regarding year of manufacture vs model year, Kawasaki (like most, if not all, other manufacturers starts building the following years models in the middle of the current year.
79 models were manufactured starting in July of 78.

As far as the GPz750's go, the only differences I am aware of between an 83 and 84 are the color scheme and the fairing mount (83 attaches to headstock with two bolts and I believe the 84 attaches with one bolt).

steell wrote:

bountyhunter wrote:

Here is how it is shown to be connected in my FSM. As shown, the spark plugs split in parallel off the high voltage end of the secondary winding. Each spark plug branch has a separate path to ground.

What year manual do you have? Both my 79 KZ750 Factory Service Manual and my 80-82 KZ750 twin Factory Service Manual (along with the 650 and 1000 manuals) don't show it that way, and my 79 manual says it covers 76-79 models.

Original factory manual for the 1979 KZ750 B4, no updates or additional model info included. Bought it new from kawi in 1979. Maroon cover with a picture of the dark red metallic colored B4 model on the cover (my bike exactly). On the cover it says: KZ750 Motorcycle Service Manual.

steell wrote:

You do realize that if your drawing is correct, then the testing procedure also given in the manual is incorrect?

Yes, if the test is to Ohm between the ends of the plug wires, it will not work. You must read from either plug wire to the +12V tap to get the winding resistance on this type of coil.

steell wrote:

By the way, the coil in your drawing won't work anyway, it's wired wrong

No it isn't actually wired wrong, since it will create a high voltage when the points open. It is wired in a configuration we call an "autotransformer" which means the primary and secondary winding are tied together. In effect, it is effectively one long winding with a tap point brought out, wound on a single core.

en.wikipedia.org/wiki/Autotransformer

The primary still induces a voltage into the secondary when the points open and break the DC current flowing in the primary. When that happens, a higher voltage is induced into the secondary winding. The secondary winding is tied to the +12V line, which isn't really much difference since the output of the HV tap is many kV.

Maybe it's only used on this one, but it's shown on the diagram in the FSM and the diagram in the owner's book that came in the bike. Both show the same autotransformer style ignition. I would think it unusual if they managed to get it wrong in two different diagrams for this bike. The diagrm is labeled: KZ 750 B4 Wiring Diagram

I'm familiar with autotransformers, but never seen one with a single tap, maybe for special uses, don't know.

Never heard of one being used by the manufacturer in any production vehicle as an ignition coil, and I've been working on this stuff for a "long" time, electronics has just been a hobby. I can't see any advantage to using such a thing in an automotive coil application, and at least a couple of disadvantages.

My 79 750 manual is two years old (part number 99997-744-04 and still available from Kawasaki as of two years ago), and my 80-82 750 twin manual was new in 82, and they both show the same pic as I posted. And Kawasaki.com shows the same coil being used from 76-80.

I don't know that the coil that was on my 79 750 when I got it was the original coil, I do know that it was a Kawasaki coil and appeared to be original, and I know that it was wired in accordance with the pic in my manual because I tested it, same as the 77 and 78 Kawasaki 750 twins I parted out, and the 79 that I sold (reluctantly, but I couldn't turn down $2500), and the two 80 KZ750G's that I have.

If you still have the original coil, have you measured the resistance between the two plug wires, and measured the resistance between either plug wire and the positive terminal?

I have two manuals (posted a pic from one, but the other is identical) and a boatload of experience that says my original statement is correct.


Edit:

Never thought to check the wiring diagram in the back of the book, but after re-reading your post I figured I would, and the wiring diagram in my book has it wrong also, it shows it like your drawing. But it's wrong and it disagrees with the maintenance section in the same manual which all my testing has confirmed is correct. So don't believe the wiring diagram as it applies to the coil because it's wrong.
And as an aside, if you read a post made by me, and it's a firm statement and not qualified (as in "I've read, I think, I believe, I've heard, The manual says," etc) then that means my statement is based on actual personal knowledge, as in I've actually personally verified that what I said is true.

My focus is turning towards the 750 fours now (although I'm keeping my 79 twin, unless it dumps me again).

These items from Z1E should go a long way toward resolving any persistent ignition problems.

Dyna Green Coils

Dyna Plug Wires

DynaS Electronic Ignition

Good Luck!

bountyhunter wrote:

Here is how it is shown to be connected in my FSM. As shown, the spark plugs split in parallel off the high voltage end of the secondary winding. Each spark plug branch has a separate path to ground.

I suspect this drawing is wrong. On the KZ's one plug is on compression and the other is on exhaust. The one on exhaust would fire at a lower voltage since it has 1/10th the gases to go through. Once it fires, the voltage drops. The plug on compression would never fire. I don't think it would ever run as drawn.

To find out is simple. Just measure the resistance from any plug wire to the primary. According to the drawing you would have continuity of some sort. But on any working KZ coil I've seen, there isn't continuity that way (primary to secondary).

loudhvx wrote:

bountyhunter wrote:

Here is how it is shown to be connected in my FSM. As shown, the spark plugs split in parallel off the high voltage end of the secondary winding. Each spark plug branch has a separate path to ground.

I suspect this drawing is wrong. On the KZ's one plug is on compression and the other is on exhaust. The one on exhaust would fire at a lower voltage since it has 1/10th the gases to go through. Once it fires, the voltage drops. The plug on compression would never fire. I don't think it would ever run as drawn.

To find out is simple. Just measure the resistance from any plug wire to the primary. According to the drawing you would have continuity of some sort. But on any working KZ coil I've seen, there isn't continuity that way (primary to secondary).

It might be wrong. I was thinking it would be unusual for them to get it wrong in two different diagrams for that model, but it's possible.

I know what you mean about the first plug firing and clamping the voltage. When I looked at it, I assumed the way it worked was as follows:

The voltage on the coil secondary builds up until it gets high enough to start arcing across one of the plugs. No current actually flows in the secondary until the arc over starts to allow flow across the air gap. Once it reaches the flash over point, current will flow abruptly down that leg. Since there is some inductance in the wire going to the plug, the very fast dI/dt current change will mean the voltage up at the coil is MUCH higher than the voltage down at the end of the wire at the firing plug. In other words, durung the time the surge of current flows down to jump the air gap, a significant voltage drop will occur along the wire allowing the voltage on the secondary to keep increasing, hopefully high enough that it reached the arc over point for the other plug.

That's how I thought it could work, but maybe it's drawn wrong.

steell wrote:

I'm familiar with autotransformers, but never seen one with a single tap, maybe for special uses, don't know.

Never heard of one being used by the manufacturer in any production vehicle as an ignition coil, and I've been working on this stuff for a "long" time, electronics has just been a hobby.

The autotransformer configuration was always the standard for conventional auto ignition coils, and still is to my knowledge.


news.carjunky.com/how_stuff_works/how_ig...l_works_ic2315.shtml

An ignition coil, which is also known as a spark coil is an induction coil in an automobile’s ignition system. This particular form of the autotransformer (an electrical transformer with only one winding and it has at three electrical connection points called taps)

This design was used to keep the voltage difference between the two windings lower and reduce arcing between them:



www.burnyourbonus.info/sci.electronics.design/thread1427.html

auto ignition coil: why autotransformer?

I want to use an old automotive ignition coil to generate a spark. I'm
puzzled that the (HV) secondary is connected to the primary.

ANSWER: Yes. It minimizes the chance that the two windings will have a high potential difference. This was much more important back when insulation wasn't so great, but it works so why change it?

Here is one reference where a guy is using a standard ignition coil for a project (diagram shown, coil is clearly an autotransformer):


www.sentex.net/~mwandel/cannon/sparky.html

An ignition coil is essentially an autotransformer with a high ratio of secondary to primary windings. By "Autotransformer", I mean that the primary and secondary windings are not actually separated - they share a few of the windings.

Here's another reference:

This place shows the Ohm test for measuring the resistance of the secondary winding on a standard auto coil:



autorepair.about.com/od/troubleshooting/ss/coil-test-ohm_3.htm


It shows the meter connected from the center (HV tap) across to the +12V terminal to measure the secondary resistance. That is an autotransformer wired coil, since the LV end of the secondary winding and the end of the primary winding are tied together.

When you think about it, a standard automotive coil has only three wired terminals: +12V, LV (points), HV (spark). If the secondary was isolated from the primary, it would have to have one end of the secondary winding connected to ground somehow. That would make the coil harder to manufacture since it couldn't be wound on the center core and just slid into the case. There would have to be a wire connected to the case somehow.

So, using the autotransformer design has two advantages:

1) Less voltage difference between the primary layer winding and the secondary winding which is wound going outward from the common tap (+12V). The portions of the winding laying on top of each other are nearly the same voltage.

2) It does not require a ground connection for return current to the windings. No internal connection to the case needed (cheaper to make) and it can't fail if the ground to the case is dirty.

That's why it has always been the standard for automotive spark.

The "floating secondary winding" topology with a spark plug on each end will work in cases where two plugs are being fired at the same time. So, it can be used in some motorcycles but would not be advantagous in automotive applications.