I'm sure it's easy but a search through this group yielded little (so far).
My mower sputters and spits, almost always at lower than normal RPMs. RPMs vary constantly, and sometimes it comes very close to quitting. It has, on a few times. This is all while on a level sidewalk, not mowing or otherwise under any strain. It doesn't change when I start mowing the grass.
I've cleaned the air filter and replaced the (very black) spark plug. I have not taken this mower in to be tuned up in the 3 years I've had it. Oh, it's a Briggs and Stratton 4.5 hp engine on a push mower (not self-propelled); garden variety Lowe's purchase.
Any ideas on what next to check, change, adjust, or replace?
Thanks.