Let's talk coils... and spark!

[ThePowster]

Evening folks.

OK so my Nighthawk doesn't run well, it never has. It's done 70 yes 70 thousand miles. It won't rev clean, it's intermittent and now it won't start at all. Today it cranked and cranked and when I stopped cranking it went psssssttt like a steam hiss 

Usually I would say non-starting would boil it down to one of two things, fuel or electrical, and I'm pretty sure it's electrical as it's so hit and miss some days.

When cranking I pulled a HT lead off and the cranking sound was no different.

So first thing we need, is information, so here is some followed by some images of my spare set of coils which I am hoping to put on the bike once we can establish if this set of coils is ok :















Right then, from the beginning....

In order to test my coils, I believe I have a Primary Coil Resistance Test, a Secondary Coil Resistance Test and a Plug Cap Resistance Test. From what I can gather so far (please tell me how far wrong I am haha) the primary test is the prongs on the back of the coil where it meets the loom and the secondary test would be where the HT leads install into the coil body and a further test coming out of the HT cap.

Am I about right so far in this being a comprehensive breakdown and test of the coil system? Please correct me if I am wrong as this will help me and everyone else wanting to check there coils.

PRIMARY COIL RESISTANCE
So my primary test, those prongs on the coils that connect to the loom of the motorcycle, my readings were as follows:

Coil 1 - 2.9 ohms
Coil 2 - 2.9 omhs

Great well at least that means they are reading the same, now let's reference the literature.

So the spec for the resistance that I am looking for is :

2.7 omhs +/- 10%

If we say plus 10% that would be 0.27, making it 2.7 + 0.27 = 2.97 ohms and mine are 2.9 so I would assume then that both my coils thus far are healthy? 

SECONDARY COIL RESISTANCE 

This resistance test is taken at the point where the HT leads screw into the coil body, my readings are as follows:

Coil 1 - 14.30 ohms
Coil 2 - 14.30 omhs

Again I am pleased to see these were the same, and I am not sure if these are called megaohms or something, but these figures did dart around a lot unless I was in a specific place and very still, so these points of contact will need cleaning.

Right onto the literature let's see what it says, I am excited as I am learning this as I am typing and I don't know at this moment what the spec should be lol.

So the spec for the resistance that I am looking for is :

14k omhs +/- 10%

So again can we assume that so far these coils have passed the test and are therefore healthy?

PLUG CAP RESISTANCE 

So I tried the plug cap resistance and I got no reading whatsoever from the multimeter, so again, can we assume that the HT leads and/or HT caps are shot? Clearly ohms are not flowing from the coils down the HT leads through the caps. 

So if I have understood this whole process correctly, these spare coils I have are fine and healthy, however they do need a clean on the contact points and I am going to need new HT wires and caps and I should be able to tick this one off and move onto other parts of the electrical / spark system.

Should all that logic make sense, my next question is, ... Performance. What would be the thickest HT wires I could get? I think this uses 5mm? I think I can get 8mm, would this be a good idea? Also what brand, and can I go all straight HT caps or do I have to have those 90 degree ones, I hate those, they are hard to get out of there.

Anything I should know about assembly of new leads and caps? 

I'll continue to update this post with other tests of the ignition system and the pulse generator which I know from when I got the bike it had black like tar coming out of the connections that go into the box, so that is very suspect too.

[Bob H]

In order to test my coils, I believe I have a Primary Coil Resistance Test, a Secondary Coil Resistance Test and a Plug Cap Resistance Test. From what I can gather so far (please tell me how far wrong I am haha) the primary test is the prongs on the back of the coil where it meets the loom and the secondary test would be where the HT leads install into the coil body and a further test coming out of the HT cap.

Am I about right so far in this being a comprehensive breakdown and test of the coil system?

Yep, that is the way to do it.
I have the later model NH 750, however my readings were about exactly the same as yours.
My manual provides a range, mine were in range, yours are in range.

When you go to replace your leads, most of the products are not solid copper core because modern vehicles are fuel injected - ECU controlled and they cut down electrical interference by using a carbon core wire.

Our bikes came with solid copper core wires. In the USA I got these https://www.napaonline.com/en/p/BEL700172
Part #: BEL 700172
Line: Belden

They list the fitment for TRACTORS and FARM EQUIPMENT because California outlawed the sale of wires that emit interference for street use...
I installed them and they were fine except that you have to cut them to length, and the supplied rubber boots are designed to "push onto" a vehicle coil. Ours are different, they have plastic caps that thread on, with inner seal. I just cut the tip off the supplied rubber boots so they were the same approximate size as the original inner seal and used that.

The factory Honda leads are designed to push down onto a spark plug that does NOT have the silver thing screwed onto the spark plug. If you pull your leads, you will see a small threaded end on the spark plug. I had to gather some of those metal things that screw onto those threads so that the leads would push down onto the plugs with snug fit. They worked fine.

[ThePowster]

Thanks for the info there Bob and the confirmation I'm on the right track too.

I was thinking with the width of the HT wire, they do say thicker is better, but I don't think the coils will take a greater wire than can be screwed into the coil, so I think I'll be stuck at industry standard which I'm thinking is about 5mm, I'll have to measure and check.

I'll update what I can source in the UK. My first step will be to consult the NGK catalogue and see what kinda specs the OEM stuff is and then see if I can source a better aftermarket set. I would love nice red ones.

[Bob H]

I was thinking with the width of the HT wire, they do say thicker is better, but I don't think the coils will take a greater wire than can be screwed into the coil...

I have never heard that. As long as you are solid copper wire core, you are good.

I think the diameters (including insulation) are fairly standardized. The ones I got did not have color choices (they were a dark gray). I did not really want them to stand out anyway.

[ThePowster]

Years ago I remember something called spitfire sparkplugs, the electrodes had a V shape in them and they had an iridium core, they boasted about better performance. I bougut some for my R1 and I felt it actually made it slower so I went back to standard.

At the time.i was searching HT leads and I think there was one called Magna core or something and I remember reading back then about performance leads for better insulation, performance, mpg and spark.

I think that ultimately though, the size of the wire I get will be determined on the width of the hole on the coils. If it's only 6mm wide there's no way I'll cram a 8mm wire in there, and even if I did, I doubt I'd get it in the HT cap.

Still it's all good knowledge finding out. Once I've measured later I'll have my answer. I'm guessing I'll be stuck with a 5mm HT lead so then I'll search for a performance one, if they do one. I guess by performance they'll mean better insulated by a thicker outer, but I doubt you'll get more copper in there.

I'll let you know what I find out 👍

[Bob H]

In these modern times, much of what you will read about spark plug wires will relate to a COMPLETELY DIFFERENT ignition system than your motorcycle.

As you look at what wires to buy, you will see terms like "Spiral wound". You will see slightly higher prices for slightly larger diameter conductors. Those are not solid copper conductors.

A lot of the spark plug wires you are seeing offered for sale will go on a vehicle with "High Output" ignition systems. The coil kicks ass and is able to shoot that spark through a carbon core (not solid copper). Those vehicles typically will be fuel injected, everything is controlled by a computer (ECU) and doesn't want the electrical interference caused by solid copper wires.

Many of the people commenting on Quora were not born when separate coils put out the feeble spark that our coils produce. Just find some solid copper coil wires and ride it. Our coils like solid copper because our coils are not putting out the juice that a more modern coil produces.



The following reference talks about cars with a distributor
(our motorcycles don't have a distributor but nonetheless this is a good explanation of types of coils, and how they have evolved over the decades).
https://www.jdpower.com/cars/shopping-guides/what-is-an-ignition-coil
Types of Ignition Coils
Conventional Ignition Coils: Conventional ignition coils, also known as canister-style coils, have been widely used in older vehicles. They are typically mounted outside the engine and consist of a metal canister housing the primary and secondary windings. These coils are connected to the distributor, which distributes the high voltage to the spark plugs. Conventional ignition coils are relatively simple in design and are known for their durability and reliability.

Distributorless Ignition System (DIS) Coils: With the advancement in ignition technology, distributorless ignition systems (DIS) have become more prevalent. DIS coils are typically mounted directly on the spark plugs or close to the spark plugs, eliminating the need for a distributor. Each coil is responsible for supplying high voltage to a specific spark plug. The DIS system uses sensors to determine the precise timing of spark production for each cylinder. DIS coils offer improved ignition performance and efficiency compared to conventional coils.

Coil-on-Plug (COP) Ignition Coils: Coil-on-plug (COP) ignition coils take the concept of DIS coils a step further. In COP systems, each cylinder has its own ignition coil mounted directly on the spark plug. This configuration eliminates the need for spark plug wires and provides even more precise and efficient ignition. COP ignition coils offer enhanced spark energy and better combustion control, resulting in improved engine performance and reduced emissions.

Also see this re: type of wire, spiral wound, etc.
https://www.motortrend.com/how-to/ctrp-0308-hei-ignition-spark-plug/

[ThePowster]

Brilliant Bob thanks for that, helps me a lot and saves me making a mistake and spending more than I need to. Cheers 👍

[Bob H]

The outer spark plug wires on stock 4 cylinder has angled boot. Aftermarket boots worked fine





Next image shows aftermarket boot, solid connection from manufacturer with wire to fitting and boot secured.
To the right is the factory boot, which has smaller inner diameter



The stock spark plug leads (on my bike) push onto threads on spark plug.
I had to place the thread-on adaptor to the spark plug tip. Same as my lawnmowers and chainsaws.
The plugs were only a few months old and I didn't want to disturb the recently torqued plugs, so I just added the tips and tightened them down with pliers as best I could in place on the bike.



In the USA I got these https://www.napaonline.com/en/p/BEL700172
Part #: BEL 700172
Line: Belden

Honestly the new plugs and wires made no difference ON MY BIKE which simply means they were not a problem.
I had done the coil mod a month earlier, and I think that did make a slight improvement at low RPM up to 4,000 or so. It was a subtle change, not as noticeable as my carb jet and diaphragm change which opened up my power to redline (previously would rev but reluctantly)

[ThePowster]

This is all very useful and interesting, thanks a lot Bob.

Much prefer the straight plugs too, those 90 degree ones can be a pain as they don't fit right, much easier to pull off straight and it's what I'll opt for.

[Bob H]

The spark plug end of the wires I got were very solid from the factory.
It is the other end of the wire that you cut to length, where it pushes into a spike inside the coil receptacle. I stripped off a bit, flared out the wires to center the spike. I didn't want the spike to miss the wire and stab the insulation.



You have to get the factory "screw on to coil" connector off the old wire. My 1993 model had a seal CRUSHED over the wire, I got it off with soapy water and pliers.



Rather than try to re-use the old seal, I cut the end off the newly supplied rubber boot (that would push onto a car coil, ours are different).



Again soapy water to enable the newly cut rubber seal to slide onto the new wire, using the old Honda threaded cap that screws onto the OEM coil

[draser]

I bought HT wire in bulk of off the internet, here in the States it's called Parker wire. The term "solid core" is improper as it's actually "stranded copper wire" - see NEC (in the States) for proper naming. Reason for buying bulk was cost and quality, as I like to see what I'm using for my HT leads.
Mounting onto the coils - I'd cut the cable flush (just like factory) and install into the coil tower. You don't want the copper core longer and flared as any and all of the copper spikes will create a Corona effect during the spark and less energy gets through, and spikes may scratch the inside of towers creating future discharge paths. The high voltage flows differently than low voltage.

[ThePowster]

Afternoon guys.

Ok so I've finally got round to taking the coils off the Nighthawk and I think the ones that were on it were no good. I can't get a steady ohms reading from one of the coils.

So I am just assembling and cleaning my tested set but I'm not sure now where the coil wires go to as in which plug they go to?

The manual shows left hand side coil powering plug far left of engine and the next one too it, problem is mine never came off that way.

Does anyone know which HT lead off which coil goes where.

Eeeekkkkk


Thanks 👍

[ThePowster]

Now I'm guessing here, so I hope it's right.

Left coil #1

Left goes to spark plug 1
Right goes to spark plug 4

Right coil #2

Left goes to spark plug 2
Right goes to spark plug 3

Sounds an odd firing order to me that 🥴

[Bob H]

...but I'm not sure now where the coil wires go to as in which plug they go to?
Does anyone know which HT lead off which coil goes where.

This is from the 1991-2003 model 750 manual but I believe yours are the same



This next image may give you clues. I used White-Out to mark the coils, and marked the leads with home electrical labels that are quite weatherproof.
I labeled mine when removing the original leads.

[Larry Fine]

Sounds an odd firing order to me that 🥴

It's really not, though. In-line 4-cyl engines fire either 1-2-4-3 or 1-3-4-2.

The two outer pistons ride and fall together, as do the two inner pistons.

In either case, cylinders 1 and 4 alternate, and cylinders 2 and 3 alternate.