Howdy!
I just received a three year old B&S 3.5 horsepower mower from a friend. Currently, it starts easy but starts pulsing once it's been running for a few minutes.
I've been told that the mower ran fine until it was tipped onto it's side to be cleaned out.
What I've done so far... - cleaned the sponge air filter - drained the gas and filled with new - sprayed the carb with carb cleaner - checked oil levels - ensured that the throttle moves freely
The only thing that I can think of is that it's internal to the carb, or that the springs on the carb are not in their correct location.
Photo's of the carb and linkage.