Spark plug/cap fitting differences?

I was in need of changing a spark plugs so I bought some iridium ones (title code). When I took the old ones out I noticed that the end that goes into the cap is different to ones I bought. I replaced them anyway (about 600miles/2months ago) and all been fine (however cap didn't fit perfectly). Now my Sv (curvy) is suffering from misfiring when engine is cold,when it worms up it's all fine. It is misfiring when trying to accelerate above 4k revs. Do you guys reckon that is the problem? I did some search job in here and some say it might be ht leads/coils? Also when engine is worm my idle drops from ~1200 to ~950 every 10s or so. Not sure if problems are related or not. My mate told me that carbs may need balancing/synchronising. Any help appreciated!!!

Plugs I bought

Plugs that I took out of the bike just not iridium.

Kind regards

That's a cap on the end, you can unscrew it & the leads will then fit properly

Originally Posted by HoL

That's a cap on the end, you can unscrew it & the leads will then fit properly

thanks for that

Lol, I had mine in & out at least three times before Google rescued me

Originally Posted by HoL

Lol, I had mine in & out at least three times before Google rescued me

I'm glad it's not only me than lol

Hmm, I can't remember at all but I have an ominous feeling that I may have done exactly the same thing! Working ok just now but think I'd better take a wee look in the next few days - the prospect of faffing around behind the radiator again feels me with joy...

Originally Posted by sputnik

faffing around behind the radiator again feels me with joy...

I know that feeling