I believe the recommended cleaning for these filters is to clean them
thoroughly and let them dry. Once dry they should be lightly oiled.

It's quite possible that residual moisture in the filter got sucked into
the engine and basically shorted out the spark plug. My advice would be
to remove the spark plug and clean it and make sure it's dry. Pull the
engine over a few times with the plug removed to vent out anything else
in the cylinder and replace the plug.

If the filter was supposed to be lightly oiled, you should do that as
the oil is sticky and traps the dust that the sponge can't by itself.

Robert

John L. Jordan wrote:

I very recently bought a brand new walk-behind mower powered by a
Briggs/Stratton 4.5 hp engine. The first time I cranked it
(pullstarter), it cranked on the first pull. The "first crank"
operation continued until I cleaned the foam airfilter (warm soapy
water and rinse thoroughly). I got the clean filter dry first by
squeezing out all excess water and then by continuing to squeeze it in
a handful of dry paper towels. When I replaced the filter it was very
slightly damp. The engine cranked on the first pull. It ran just fine
for a full minute then died. I cranked it again on the fourth or fifth
pull. Same result. One minute of smooth opp, then it died. I've just
cranked it for the fourth time with the same result. If the foam
airfilter wasn't perfectly dry, would enough moisture have accumulated
somewhere to cause this problem? If so, how do I remove a few droplets
of water from the system? I have run this engine for less than 3 hours
in very dusty conditions. The fuel tank vents are clear.