which one you change one step colder? did you have the reference? to be honest i already have iridium installed, on idle i feel little diference. but may i return to the stock one or even little colder, depend your reference.
NGK IX iridium 4469 LFR5AIX-11 .044"
NGK Double Platinum 6240 PLFR5A-11 .044" (Original Equipment Manufacturer, and/or Original Equipment Service Part)
Note: i was checking the gap of the spark splug today, looks clear, but on the rock of each spark have a little oil, is normal in this engine, or is evidence that the cam gasket is permit pass oil from seals of o-rings? remember the oil is not on the gap of the spark, just around rock.
the gap is ash by the use of LPG.
Gasoline leave Carbon residue because is not burn entirely on the cylinder just 70% of mixture is aproach.