The pilot system is what provides fuel when the slide is closed (idle position). It consist of the pilot jet and airscrew. It also provides fuel at other throttle positions but its effect is dramatically diminished as the throttle is advanced. A clogged pilot system will cause hard starting and rough idle.
Ethanol fuel is no reason to change pilot jet size. It has nothing to do with the temp of the engine.
There is rarely a need to change from stock pilot size with a stock engine/carb.
An explanation is in the H manual pg47
http://www.3cyl.com/mraxl/manuals/hseries/sec3.pdfIf highest idle rpm is attained with airscrew adjusted between 1 1/4-1 3/4 turns out then you have the correct size pilot jet.
http://www.3cyl.com/mraxl/manuals/carbt ... #adj%20low