I ran my XTR with the iridium plug CR7EIX for a tank full and the fuel consumption increased compared to the standard plug and the engine just did not feel right compared to the original plug I swapped the iridium plug from my xtz and tried it in the XTR no change the engine just did not feel right compared to using the standard plug that was fitted, when checking the plugs I realised that the original plug fitted in the xtr was a CR8E not a CR7E as recommended in the owners manual.
I refitted the 8 back into the XTR and the engine is running much better now got another CR8E plug and replaced the CR7EIX that was fitted into my Tenere and B****r me now she is running better than ever.
I have never come across this where a plug one grade hotter or colder made such a difference, the CR8E is a slightly cooler running plug
I am recording my mileage on both bikes on the Fuelly web site
I am going to stick with the 8s and I wonder has anybody else come across the above