Poor Spark query ??

Let's go back to the basics of troubleshooting. To isolate the problem part in a system that has multiple parts alike, just swap the parts around and see if the problem travels with a particular part. In this case, if the lead lengths allow, just swap that number 5 cylinder's lead with the other cylinder running off the same coil. Sounds like it could be a burned out section of the #5 lead! But, that would also diminish the spark intensity of the other cylinder running off the same coil since spark intensity is a matter of current flow and any increase in resistance would affect BOTH leads! Now, if the insulation in the #5 lead were breaking down and leaking some of that spark to ground, it would still allow the other cylinder on that coil to run fine. But, there would be a really ugly burn mark at the point of leakage, if not a hole in the insulation.
Talking about electrical stuff on forums, in print, is extremely hard since, yes, it does appear to be a black art form. LOTS of stuff to understand about electricity to really have a "feel" for what's going on. I've spent my whole adult life playing with electronics and electrical stuff and just wish there was some way to plug a USB cord between our brains to share all that experience!

Kawboy, pretty damn good explanation, but a lot of possibilities left out! And here's where it gets complicated to explain in print on a forum. But, just one possibility would be if the insulation of one spark lead were to break down and leak to ground, that would weaken the spark energy to that plug, but COULD actually decrease the overall resistance in the WHOLE circuit, causing a stronger spark in the other lead from that same coil. Gotta keep in mind that if all parts of the circuit are in good shape, the current in all sections of the circuit will be the same, meaning that the spark intensity will be the same. But, shunt some of that energy to ground at any point and you imbalance the system, causing one spark to decrease and the other to possibly increase from a decreased resistance in the system overall.

There would be about three more volumes to cover all of the other possible issues that could happen in these silly double-ended coil systems!

BTW, somebody on here was talking about their bike popping on deceleration recently. This "wasted spark" system is partly responsible for that, too! When you close the throttles, there is an initial small surge of fuel that has no air to burn with it, so when the exhaust opens up it goes out unburnt. Well, that "wasted spark" sometimes catches the tail end of that batch of fuel and ignites it along with some of the incoming air/fuel during the valve overlap period. There is a lot of air in the exhaust to allow for combustion, so you will get a pop once in a while, or when all conditions are favorable, a LOT of the time! Just watch the exhausts of some of the higher-powered GT race cars as they enter a turn. Their valve overlap is so great that they burn a LOT of wasted fuel this way, and it causes more than just a simple pop! Huge flames shoot out!

Oh, we could go on and on, but,......!

Kawboy wrote: Sure would be nice if we could entice Trikebldr to churp in here. He IS our Guru of ignition.

this wasted spark system is a bird of a different feather. The spark leaves the coil and travels down the one spark plug lead which in the Kz1300 is a solid core lead. Since it's a solid core wire, there will or should be no resistance in the wire. Next it goes through the spark plug cap. Now most of the spark plug caps used are 5K ohm resistance caps BUT, somebody could have changed out the 5K ohm cap for a 1 K ohm resistor cap or a 10 K ohm resistor cap or it may not have any resistor in the cap. On the stock cap, the resistor can be removed by using a screwdriver and removing the brass insert that attaches to the spark plug. The resistor can be taken out and checked. If I remember right, there is also a small spring in there as well. The purpose of the resistor was to reduce electronic noise when we used to use "copper core " spark plugs (which have no resistance).

Next, we go into the spark plug with the spark and down the center electrode. Most resistor plugs if I remember correctly are 10 K ohm plugs, so if you measure from the top of the plug to the center electrode you should measure 10,000 ohms and from the top of the plug to the base an open circuit. It is possible to measure resistance between the top of the plug and the base if there's carbon tracking on the ceramic on the center electrode or if by chance there's a crack in the plu

Next the spark jumps the air gap in the first plug. Depending on heat, humidity, fuel mixture, spark plug gap and amount of compression the effective resistance across the plug could be anywhere from 15K ohms to maybe 40 K ohms. Then the first spark occurs.

The spark now travels through the ground plane which most likely is the cylinder head reaching the other plug in the circuit to the coil that fired the first plug and jumps from the ground electrode on the second plug to the center electrode. The next stop will be the resistor in the second plug (10 K ohm) then in to the second spark plug cap and through what should be a 10 K ohm resistor and then up the solid core wire returning to the coil where the spark was initiated.

So we know that resistance is trying to impede the spark and the spark is just trying to make it's journey. At any point in the circuit where the spark meets resistance work is created to over come resistance and the result of work is heat but also there's only so much energy sent in the spark and anywhere that the spark encounters work energy is expelled to overcome that resistance.

This is why I hate wasted spark. ANY point in the circuit that has resistance can cause a loss of energy across one of the plugs due to a high resistance in the circuit. you have to realize that it's a complete circuit and the spark is trying to complete it's mission which is get from one end to the other which is out one terminal of the coil and returning to the other terminal of the same coil. You really can't JUST say if the one plug is firing then the weak spark is on the bad wire from the coil. If you make that judgment then you're of the believe that 2 sparks are going down the 2 wires and jumping to ground and that is definitely not the case in a wasted spark system.

I hope this explanation makes sense and causes those out there to realize how very different this ignition system is to the standard single spark system.

Excellent description and accurate schematic. Kawboy, your engineering knowledge always impresses!

Tonto, Please heed trikebldr's advice. He has given you the advice needed to find the problem. Almost certainly, one half of the wasted spark circuit has either too much resistance, or a leak to ground.

One thing to consider is that the negative polarity spark plug will always require more voltage to jump its gap than the positive polarity plug. This is because electrons move easier from a hot to a colder surface. The center electrode is at a higher temperature than the ground electrode.

Thus, anything that reduces the voltage in the circuit will have a greater effect on the negative polarity spark plug.

Thanks very much guys, for some very helpful guidance: its appreciated.
I spent most of my working life operating a pen, and then later a keyboard, moving words around on pages, and am grateful for access to the years of collective experience that abounds on the forum.

I am going into the garage later this morning, to top up my auxilliary fuel tank and have another go at resolving this. Sometimes the simple things dont appear so simple until someone points it out to you :oops: like I never thought of even swapping HT leads 1 & 6 over, just to see if the fault moves with it.

Once again, thanks for the words of wisdom.

Cheers Tim