Spark plugs.

A couple of weeks ago I woke up the big Zed from its winter hibernation. I always follow the same procedure. I drain the sump and put in fresh oil and a new filter, remove the empty fuel tank, take out the spark plugs and shoot a generous squirt of WD 40 down each cylinder. Then I whir it over a few times, replace the plugs, fill up with fresh fuel fingers crossed it starts up with a cloud of smoke then settles down to an even tickover. I went out for a ride last weekend and I couldn’t help noticing something wasn’t quite right, nothing too bad, but it just didn’t seem to be pulling as hard as I remember from last year, and it seemed to have a slight misfire. I rode it home, and the first thing I did was to check the temperatures of the down pipes. I have one of those laser / infrared type digital thermometers. If any of you don’t have one I would advise you to add one to your tool kit. They are cheep as chips on the internet; mine was less than a ten pounds. This confirmed cylinder number two was running quite a bit cooler then the other five, still hot, just not as hot as the others. I checked the plug and it was a bit black and wet with fuel. I use iridium plugs, and the bike has had the same ones for about four years, they’re supposed to last for about fifty thousand miles. Now here is the strange thing that I have never encountered before. I held the plug against the cylinder head and ran the engine to check for a spark, but instead of a nice big spark all I got was a bit of smoke from the electrode. I gave it a couple of revs, still some smoke but no spark. I changed the plugs and it is now running sweet as can be, and back to pulling like a train. Any of you techy boffins out there have an explanation for smoking iridium plugs?

If I had to guess, I'd say the spark was so weak as to not be visible, but still enough to produce a tiny bit of heat to burn off the oi/gas on the weak plug.

Well Mc Zee, you forced me to look up "Boffin"

bof·fin
ˈbäfən/Submit
nounBRITISHinformal
a person engaged in scientific or technical research.
"a computer boffin"
a person with knowledge or a skill considered to be complex, arcane, and difficult.
"he had a reputation as a tax boffin, a learned lawyer"
I'm somewhat smarter now but not sure I fit the noun Boffin although I did have 10 nuclear engineers reporting to me.

if I had to take a stab at your finding I would say the center electrode insulator was covered in a film of oil and the spark was traveling down the side of the insulator to ground (that being the body of the spark plug and as it traveled through the oil film which was conducting the current since the oil carried some carbon deposits, the oil was smoldering making the visible smoke. Electricity will always take the line of least resistance so rather than jumping the air gap to the ground, it would choose to take the line of least resistance. Had you taken a can of starting fluid (ether) and sprayed the sparkplug washing off the oil residue and then let it dry. You probably would have saved the plug and your blue spark would have reappeared.

Lol
I forgot about the differences in the English spoken across the pond. It was strange to see the plug smoking away and not a trace of a spark. I’m now not 100% convinced about the advantages of iridium plugs, although I must admit I’m an advertisers dream. All those snake oils you read about in the biking press, the sort you add to your fuel, or those oil additives If I read about a product that claims to make your bike run better then I’m almost compelled to give it a try, I just can’t help myself.
A mechanic recently told me that iridium plugs were very good, but he said that when they fail they seem to just suddenly cut out, and need to be replaced.
Any one on here have any thoughts on the advantages or otherwise of iridium plugs?

I've been using Iridium plugs for as long as they've been available. I'll use nothing but them. They are the cleanest burning plugs I've found. 100,000kms plus on a set in the cars.
That being said, how's your oil consumption? I'm wondering if maybe you're using oil and possibly #2 cylinder is the worst. I suspect intake valve seals may be the culprit. Piston rings are not out of the question but usually once there are broke in, they usually do their job for a long time. Valve seals on the other hand get brittle with heat and go hard, then fail.

My only experience with iridium plugs has been in my 01 Busa and they were lousy they fouled up within 100 kms so back to standard plugs in it my 13's are still.works in progress at present so no experience in them for me