3rd cylinder refuses to fire.

[BeardedShooterUK]

Afternoon chaps.
I've got a 2000 FZS600 and the 3rd cylinder simply refuses to fire.
What I've done so far is fresh spark plugs, some used but working OEM coils with caps, I've had the carbs off and cleaned all the jets (3rd carb was actually blocked so I thought I'd solved the problem but nope) a compression test (with throttle fully open) and all 4 cylinders are within a couple of PSI to each other at around 175 which from my research is perfectly healthy. 
I've cleaned all the connections that I know of and have located from the battery all the way to the plug caps.
I've tried petrol down the cylinder just to see if it would fire at all.
I've tested the spark on cylinder 3 coil/plug and it's not the biggest and strongest spark I've ever seen but in my opinion it's strong enough to at least ignite the cylinder especially with a drop of fresh fuel.
The carbs are definitely getting fuel as is the cylinder because the carb bowls were all full after the rebuild and test.
I really can't think of anything else. 
I don't really have the spare cash at the moment to put it into a garage but I'm also wanting to try and fix it myself to learn as I go.
The only thing I haven't changed is the battery and it is a bit on the dodgy side having been run dead previously but after a good charge it fires all the other cylinders within a second or two of pressing the button.
Is it possible that could be the culprit and it's only effecting a single coil wire/plug cap?
I'm really wanting to get back on the road as a friends just got back into biking as well as my Mrs wanting to go out for rides as pillion.
Any suggestions would be very appreciated.

[Gnasher]

Check the HT lead, the plug cap and plug. The coil shouldn't be the problem as each coil fires 2 cylinders, in which case both wouldn't be firing if it was a coil. From memory the HT leads are bonded into the coil pack, the issue with these is at the plug cap end. Unscrew the cap and check the lead. If they need trimming be careful you don't trim too much, as mentioned the coil end is bonded.

To check the cap swap it for one on a cylinder that's firing and the same with the plug, remove it and put it into t a firing plug cap.

[BeardedShooterUK]

Check the HT lead, the plug cap and plug.  The coil shouldn't be the problem as each coil fires 2 cylinders, in which case both wouldn't be firing if it was a coil.  From memory the HT leads are bonded into the coil pack, the issue with these is at the plug cap end. Unscrew the cap and check the lead.  If they need trimming be careful you don't trim too much, as mentioned the coil end is bonded. 

To check the cap swap it for one on a cylinder that's firing and the same with the plug, remove it and put it into t a firing plug cap.

It's had all that swapped but I suppose it's possible the new/used ones aren't performing to their full potential. 
When swapping plug caps it then runs on 2 cylinders.
That led me to think changing the coils, ht leads and plug caps would sort it, but I was wrong. 
I'll try trimming the wires very slightly and try that.

[coeurdelion]

Afternoon chaps.
I've got a 2000 FZS600 and the 3rd cylinder simply refuses to fire.
What I've done so far is fresh spark plugs, some used but working OEM coils with caps, I've had the carbs off and cleaned all the jets (3rd carb was actually blocked so I thought I'd solved the problem but nope) a compression test (with throttle fully open) and all 4 cylinders are within a couple of PSI to each other at around 175 which from my research is perfectly healthy. 
I've cleaned all the connections that I know of and have located from the battery all the way to the plug caps.
I've tried petrol down the cylinder just to see if it would fire at all.
I've tested the spark on cylinder 3 coil/plug and it's not the biggest and strongest spark I've ever seen but in my opinion it's strong enough to at least ignite the cylinder especially with a drop of fresh fuel.
The carbs are definitely getting fuel as is the cylinder because the carb bowls were all full after the rebuild and test.
I really can't think of anything else. 
I don't really have the spare cash at the moment to put it into a garage but I'm also wanting to try and fix it myself to learn as I go.
The only thing I haven't changed is the battery and it is a bit on the dodgy side having been run dead previously but after a good charge it fires all the other cylinders within a second or two of pressing the button.
Is it possible that could be the culprit and it's only effecting a single coil wire/plug cap?
I'm really wanting to get back on the road as a friends just got back into biking as well as my Mrs wanting to go out for rides as pillion.
Any suggestions would be very appreciated.

Hi ,have you tried running in the dark to see if there's anywhere between the coil and the cap that's is sparking out and earthing before reaching the spark plug?
coeurdelion

[BBROWN1664]

swap the coils over to prove the fault stays or moves with teh swap. that will prove the coils and carbs at the same time

[BeardedShooterUK]

I'm hopefully going to have another look at it this Friday or weekend and shall report back.

[BeardedShooterUK]

Brand new battery on, still not firing.
Tried changing the plug cap and trimmed the HT lead a bit until I got to nice fresh wires, still won't fire.
I'm honestly completely at a loss now, with no ideas at all what to do.

[BBROWN1664]

Did you swap the coils over to prove its not that?

Left coil connects to cylinder 1&4, right connects to 2&3 but they are both identical so just swap all the connections over to test it.

[unfazed]

If you are happy that it is not the Carbs and you say you have a weak spark in three then the most likely cause is corrosion within the plug cap and 3 is the most prone to it.
Remove the plug cap and test the resistance within it, It should be around 10Kohm but when corrosion gets in they can got to Megohms and the simplest solution to clean the internals.
The reason 3 is most prone becaue if on the side stand this hole fills with water and and does not always drain out the drain hole as the hole gets blocked
Looking in at the bottom of the plug cap you will see a slot for a screwdriver, unscrew this then a resistor, a tiny spacer (about 5mm diameter and verr thin) and a spring will fall out. If the spring does not come out it is stuck and will need a bit of twisting with a small screwdriver to dislodge it. Check the resistance of the resistor as this is where your 10kohm will be that can go faulty. On the screw in part, poslish off the corrosion off the flat end until you have shiny brass.. Then try to polish the spacer, if it breaks try and use something else as it saves the resistor from damage from the spring, but it will work without it for testing. Clean the spring and finally with a sharpened screwdrive or something like it clean/scratch the corrosion off the flat brass surface inside the plug cap.
Put it all back to gether and test it. It should now be around 10Kohm