if the sparkplug is to cold i will get black and in time the spark will be harder to jump.
If the sparkplug is to hot the fuel/air mixture can self ignite before the spark plug makes a spark and this can my time melt a hole in the piston i think.
Is the sparkplug thread is to long it can hit the top of the piston.
If the sparkplug gab is to big the spark might not jump.
If its to small a gab the spark might to to weak.
I pretty sure the right sparkplug for your scooter is NGK CR7HSA wich is called a standard sparkplug.
If you want to exchange the standard NGK CR7HSA plug with a plug with iridium you can look for NGK CR7HIX or Denso IUF22.
I wanted to use a Denso IUF22 in my Kymco Super 8 (50cc) but i could not find any dealer in my area that could get it.
If you drive short trips in the city and low revs most of the time instead of using a CR7HSA you can use a CR6HSA. This i called a HOT sparkplug and will burn off the black carbon build up more easyly.
If you drive fast and long trips and high revs you can use a CR8HSA instead. This is called a COLD sparkplug because it trafers heat away from the plug faster.
You can have a look at the pictures here and maby use google translate to the right if you want to read the text :
http://scootergrisen.dk/scooterhjemmeside/tandror.phpThe answer to your question... yes it will have a performance effect.
