Hey guys, this is my very first post on the forum. I would like to thank everyone in this thread for asking and answering some great questions. By just reading through and keeping up with the new and old post I have been able to tune and run my GO engines without any problems. Well, until recently. Not really a problem but more like just confused. Here's the deal, since day one of the purchase of my GX5, GX7 and MG66,s I've only run Odonnell 97t plugs as per what most recommend and they all have performed flawlessly. Just for S&G's I put an OS P3 in and "WTF", my engine started running rich and wouldn't clear out. My temps went from an average 255* and running like a scalded dog to 205* and running like a dog. All this was just from a plug change and not messing with the needle settings. After a retune (3 hrs. in on top and 1 hr. in down low), I felt as if I had a brand new motor. Ended up having tons more bottom end and loads more top end that wouldn't stop. Another thing is that my head temps went down to 245*. I have since done this to all of my engines and the results were all the same. Not complaining or anything, just looking for an explanation as to why putting a hotter plug would cause me to lean the needles an have more power with lower engine temps.
more power-lower temps-longer tank times

BTW: Shim stack is .4 (1 silver and 1 copper) on A-Main 25%