The plug does not have alot to do with it holding a tune other than good plug bad plug. Tune is mainly air + gas if you get that right whatever plug your running is already factored in. RB's are well known for holding a tune like a vise. Also they like it slightly rich on the lsn. tune lsn 1st then your hsn setting will be a breeze. I can call my temps with a simple turn of the hsn and generally be correct within 5-10 degrees. RB's take atleast a gallon for true breakin and to show you it's real power the one drawback of the rb. If you can call that a drawback however that also coincides with there long life. True break in is when the engine is up to temp remove the plug and turn the flywheel there should be little to no resistance at tdc. With plug in it should always be difficult to turn over thats called compression and thats a good thing.

My suggestion is to follow the rb breakin run it slightly rich for then entire gallon and always and I mean always have it up to temp atleast 220. Preheating the enging before starting is a + and generally necessary on the first few starts. Running an engine below temp less than 200 is as bad or worse than running it too hot. Cold engines actually generate more wear due to the nonexpanded sleeve rubbing against the piston. Correct operating temp causes sleeve to properly expand and allow the piston to move up down with minimal wear against sleeve. RB's perfomance range is 220 - 260 some run hotter I have always generated good to great power in this range. I generally run mine at 240 for just practicing and 250-260 for races. Keep in mind every engine even of the same type (S5) will be as different as a fingerprint. Some will like it hotter some will like it cooler no two engines are the same.