Originally Posted by Bikeguy Joe
Think of it this way as well- @40:1 you have more than twice as much gasoline in the gas/oil mix, and that means a 'richer' carb setting.
Which is all too often overlooked when trying to tune a carburetor.
It's very simple. Oil doesn't burn therefore whatever oil is in the mix, if decreased, means more of the mix is gasoline. More gas means a richer fuel to air mix. Decrease the amount of oil and you'll need to decrease the mount of fuel to the fuel/air mix for an effecient burn.
This is where folks get in trouble running the exotic 100:1 oils. To get the engine to run right they go lean on the fuel to air mix but often overdo it and end up with a damaged engine. Then they blame it on the oil.
2door just shakes his head and walks away.