Our award-winning DragonFly™ stove has a fully adjustable flame, which makes simmering a breeze. However, with other MSR liquid fuel stoves, the most efficient way is to run the stove with extremely low pressure in the fuel bottle. A couple of pump strokes in a half-full bottle are optimal.
Here is an excerpt from a video you can find more videos online from other content creators with additional tips and tricks to master the simmer with your WhisperLite or other liquid fuel stove: Simmer with liquid fuel.