There is no easier or more complete way to keep your mower in good shape than to remove the metal carburetor bowl. Let all that gas drip out, take the bowl off and look inside. I once did this for the first time on our snowblower the first season I was running it. To my shock and horror there was a small pile of black fragments sitting in there! It appeared to be bits of vulcanized rubber or a similar substance. I freaked out knowing that any debris in that area can affect a motor adversely (especially a small 3.5hp one). I cleaned it out and it helped a little. But what I really needed was a good new accurately gapped spark plug. Ultimately it was that spark plug that made a bigger performance difference than any other. But it never hurts to remove that bowl and wipe it out. For good measure I will leave a little bit of carburetor choke cleaner in the bottom of the bowl when I reattach it. That way anything that might form there will stay in solution until the following season when I first prime and start the motor. Doing this, I usually get one big puff of grey smoke out the exhaust until it warms up. Then everything is free and clear and runs great.
Even if you’ve run your equipment dry as part of your usual end-of-season maintenance steps, some fuel can remain in the bowl of the carburetor. If you don’t drain the bowl, you might see some of the telltale white residue and related corrosion associated with ethanol blends. Four-cycle engines in particular seem prone to the buildup, although two-cycle engines can also suffer from the problem.