The MSR Whisperlite is arguably the world's best wilderness stove. While not the lightest stove on the planet, nor the fastest boiling, it has one distinct advantage over all others- simple maintenance and repair that can be done in the field. MSR has been making the Whisperlite with very few design changes since the late eighties and they are reliable and (almost) indestructible.
While they are easy to maintain in situ, I give mine a full cleaning at the beginning of any season or anytime it seems to be running a little ragged. Some signs that your Whisperlite needs cleaning are uneven or "coughing" jets, leaking fuel, difficulty starting or holding pressure, or any other problems pertaining to performance. Even if your stove isn't exhibiting signs of being dirty, it is a good idea to give it a good clean once a year. Here's how:
If you don't already own an MSR Maintenance Kit, go get one. Just the basic kit is all you need for regular maintenance. The basic kit contains extra parts, tools specific to your stove, and a helpful diagram to help you keep all the parts together. If it has been a while since you did any maintenance on your stove, the "expedition" kit might be the way to go. This contains a more comprehensive set of replacement parts, including a pump cup- a part that without regular maintenance and lubrication, can pretty easily become cracked.
I was excited to provide step-by-step instructions on cleaning a whisperlite, with beautiful, detailed pictures I took all on my own, but then a quick internet search revealed that in fact there is a multitude of info out there on cleaning these legendary stoves, including some great videos from MSR themselves. Rather not get in the way of the experts, so...
Pump Cup Maintenance and Cleaning