My mower is a bear to start I have gotten into the habit of removing the spark plug before each cold start and adding a tablespoon of gas just to save my arm. When running the mower is weak and sputters a lot, I have to stop frequently to let it rev back up and then resume cutting until it eventually stops and then I put it away until I can get to it again. So far I have replaced the spark plug the air filter and refilled the gas tank with some 91 octane and no change. I did adjust a screw on the side of the carb a few months ago which didn't seem to make a difference. When attempting to start I usually pump the primer a couple dozen times because I gave up on the three pump system when 20 something worked a few times. I have also taken the bowl apart a few times and cleaned out the orifice usually its clean (I recently added an inline filter to the fuel line from the gas tank)

Fuel filter will not work on a push mower . Not enough flow,
Remove filter , check the bolt that holds the bowl on there is two holes in it where the fuel feeds into the carb .
Luck

Hi,
My humble guess is that you have notched the flywheel key and it is out of time slightly. With the newer ignitions that are required to pass the EPA regulations, the engine manufacturers have had to make some fairly complicated changes to the armatures with builtin advance systems that are very sophisticated. Years ago the engine would not start and might try to pull your arm off at the shoulder. For the last few years I have seen engines that are difficult to crank and would run badly once you got them cranked.
Peace,
Clarke