So, here is "saw school" on running "fat"... A lean saw runs really clean, but doesn't lube as much... A rich saw rins really dirty, but lubes better... Somewhere in the middle is a saw that runs kinda clean and lubes just right (sounds like goldy lochs and the three bears)... So, running a saw fat is giving it max lube, but its running dirty. Running too fat can lead to carbon buildup and "could" damage a cylinder... What I do is to run a small amount of Seafoam in my mix while I'm running on the rich side, so it has some cleaning aspects as well as the extra lubrication. Now, 12,500 isn't running really dirty... 10,500 would be really dirty... I do notice at 12,500 and 40:1 that it will puff a little after idling for a while when you rev it up... But, 12,500 is very "torquey" for milling... I'm not cutting cookies, so I'd rather have the low end torque and the extra oil... Remember, when you are cutting firewood or bucking trees, you're in the throttle for 15-30 seconds at a time. A tank can buck an entire tree. When milling, I run an entire tank of fuel on one 11' long by 24" wide slab... You could be in the throttle for 8-10 minutes in some cases (minus a couple small breaks for wedges and fatigue)... I might run 10 tanks of gas through a saw in one day milling... Thats a year of firewood cutting for most people...