Poor Spark query ??

Chaps am I alone in finding bike electrics a mystifying and black art ?

At start up my A1 has recently started running on 5 cylinders: I initially thought was a carb issue, caused by infrequent limited use and old fuel: but when investigating further I narrowed it down to an igintion gremlin. I am getting a weak intermittent spark on plug no.6, so fitted a new plug and plug cap (can see no damage to the HT lead) but am stil has the same weak spark . I cant see its the coil, as No. 1 is firing strongly - so before I lash out on a new coil & leads or really push the boat out and upgrade to a set of Dyna coils - is there anything obvioius I should be checking out. I am hoping its not going to be the dreaded Igniter as a route cause ?

Any advice or suggestions greatly appreciated.
Cheers Tim

can not help you tim but ive got the same problems on my a 1

Tonto wrote: Chaps am I alone in finding bike electrics a mystifying and black art ?

At start up my A1 has recently started running on 5 cylinders: I initially thought was a carb issue, caused by infrequent limited use and old fuel: but when investigating further I narrowed it down to an igintion gremlin. I am getting a weak intermittent spark on plug no.6, so fitted a new plug and plug cap (can see no damage to the HT lead) but am stil has the same weak spark . I cant see its the coil, as No. 1 is firing strongly - so before I lash out on a new coil & leads or really push the boat out and upgrade to a set of Dyna coils - is there anything obvioius I should be checking out. I am hoping its not going to be the dreaded Igniter as a route cause ?

Any advice or suggestions greatly appreciated.
Cheers Tim

Just my two cents worth, however if the one lead on the coil is firing fine and the other isn't then it has to be the coil/lead as the bike's ign is a wasted spark type of firing system both leads of the same coil fire at the same time if you had said that one coil was firing intermittently I would had suspected the pickup coils as they were problematic on the 79's at least anyway

It's unlikely the coil itself has failed becuase, as you say, you'd have a similar issue on plug 1. It might be the HT lead from that coil though. Easiest way to check is to swap with one of the other coils and see if the problem disappears.

zoso wrote: It's unlikely the coil itself has failed becuase, as you say, you'd have a similar issue on plug 1. It might be the HT lead from that coil though. Easiest way to check is to swap with one of the other coils and see if the problem disappears.[/quote

In my reply I was referring to OEM coils which do not have removable HT leads (at least not on any of my 79's) if I misunderstood what coils you are testing I'm sorry.

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 plug.

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.