The reason why the carbs need re-tuned is that the ethanol in the fuel actually leans out the fuel. You need just over TWO times the volume of alcohol compared to gasoline to run a stoichiometric mixture ............... the more alcohol in the fuel, the more high and low speed opening you will need.
If any machine is tuned for ethanol fuel, then switched to canned fuel, it MUST be re-tuned to account for the different BTU/gallon of fuel.
As far as the machine not being capable of being leaned out on the high end, Has the air filter been cleaned ? Was this the 066, the 460, or both saws couldnt be leaned out ?
A great way to check without laying out any money is to remove the air filter and try to tune it again. If it leans out the way it should without the old air filter installed, its time to get a new air filter.