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ukbandit
1st February 2016, 11:11
Hi all
Bike is a Suzuki Bandit 2001
Fault is weak spark on number 3 plug.

I had done some work on the carbs, cleaned and fitted new bowl seal but I also had the headlamp off to repair a couple of cracks. The bike was running ok Without the headlamp on, after putting the head lamp back and somehow getting the rats nest of a loom to fit in number 3 cylinder seemed to not be working, down pipe cool compared to the others.
I swapped plugs, removed headlamp as I thought trapped wire earthing or something but still the same. Then after a lot of pulling and twiddling it seemed to come right, went for a blast all seemed good.
A week later same issue not firing although there is a spark but possibly to weak to do its job.
Number 2 works great and as the coil supplies both 2-3 at the same time I wondered if it is possible to have 1 side of the coil to not function properly? As far as I can tell it appears as one coil not 2 seperate coils in one case? Is that the case?
Secondary ohms 37.4kohms between plug leads for the coil.
The reading for the other coil is 38.6kohms so they are both within range 30-40kohms

Now a crude test I did was to use a current detector what you would use to detect live wires in your house, this one is a little pencil type thing.
I ran the bike placed it near each lead 1-2-4 lit up like a Xmas tree and the clicks it makes were loud, on 3 the led barely lit up and no clicks? So it appears that there is less current in that lead? Hence the question about one side failing?
I assumed the primary is working as number 2 seems fine.

Any thoughts or ideas to try would be appreciated.

Cheers
Les

jellywrestler
1st February 2016, 11:24
are the wires long enough to swap the coils over completly and chase the fault to another cylinder to prove your theory.
it sound like a wire has become detached either at the plug cap or in the coil.
if you swap tow and three does the fault follow to the new cylinder?

awayatc
1st February 2016, 11:30
Sounds like weak or faulty earth from coil....
Not sure if your coils have wee earth lead, or earth directly to frame...
either way, trace your earths....and make sure you have good and clean connections

ukbandit
1st February 2016, 11:57
are the wires long enough to swap the coils over completly and chase the fault to another cylinder to prove your theory.
it sound like a wire has become detached either at the plug cap or in the coil.
if you swap tow and three does the fault follow to the new cylinder?

I should be able to swap 2-3 leads over, I might have to unbolt the coil from the frame.
I did think of doing that but was a little confused how the coil works? By that I mean is it 1 coil or 2 coils in one? Looking at the schematic in the manual it looks as if the secondary part may be sort of split as it has 2 outputs or appears that way.

Thanks for the read and comment and I will try that to see if anything shows up.

Les

ukbandit
1st February 2016, 11:58
Sounds like weak or faulty earth from coil....
Not sure if your coils have wee earth lead, or earth directly to frame...
either way, trace your earths....and make sure you have good and clean connections

Good point I will look into that and update if I find anything.

Thanks for the read and comment.

Les

jellywrestler
1st February 2016, 15:22
If it's a faulty earth neither plug will work, could it be a faulty plug that may have a short to earth meaning no spark jump?

Motu
1st February 2016, 16:51
The earth for an ign coil is the spark plug, they are not earthed themselves. You have a waste spark system, it fires in a loop - one spark centre to earth, the other earth to centre electrode. If it's one side you have a faulty lead or plug, that's why you need to swap those for cheap diag, or the coil itself is fauly...so swap that for the other too.

spanner spinner
1st February 2016, 20:48
the coil is either shorting to earth internally or the plug cap or lead is high resistance forcing the voltage to find another part to earth. if it is the plug cap or lead leaving it like this will eventually burn a path in the coil to earth that will bypass the lead and there will be no spark at all on number 3 . see attached picture of the coil wiring which will explain more

319250

ukbandit
2nd February 2016, 10:15
cheers guys, all very helpful.
i will swap the lead to test and report anything i find for others reference.
my thoughts were that the half of the coil for that plug may have shorted windings?

Cheers
Les

Motu
2nd February 2016, 16:40
It's no half coil, but there will be an internal short on that side, check the diagram you have been supplied. It needs to complete the secondary circuit, and will do it any way it can.

ukbandit
2nd February 2016, 19:04
It's no half coil, but there will be an internal short on that side, check the diagram you have been supplied. It needs to complete the secondary circuit, and will do it any way it can.

Hi Motu
Yeah that's more or less what I meant that the winding for the faulting lead could be shorted as it shows one coil 2 outputs.
There is 1k ohms difference to the other coil, either just the way it is or maybe the lead lengths or possibly a short.
Thanks for the read and comment, I will check out some bits this week and post any findings.

Les