After many spark plug problems with different NGK plugs I have tested Denso plugs on my -02 monster 900ie.
I've read that denso plugs may work better if some problems with rich or not correct fuelling.
So now my bike is running hotter plug Denso XU22epru.
I thought hotter plug runs cleaner.
I read also about known issue on this ecu is rich running on every start. Even motor is hot. So plugs might go black.
Also need LB05e ngk spark plug cap on densos.
And next I'll test Denso XU22TT twintop sparks because they were on discount 4pieces about 5 euros.
Hope this summer goes without plug problems.
Does your bike have standard pistons?
Yes, standart pistons.
Airbox mod and open silencers.
The reason I asked was because I have seen Denso iridium plugs (equivalent to NGK) just touch the raised crowns of hi comp pistons, closing up the electrodes. Upon inspection, the Denso plugs protruded a few mm deeper into the combustion chamber than NGK or Champion plugs. This was some time ago so it may have been fixed, but check the plugs against each other carefully.