I'm losing my marbles on this one. I can concoct and build all kinds of crazy stuff but I can't keep a stinkin lawn mower running.

I've got a 5 or 6 year old Husqvarna push mower with a B&S engine (metal carb, not plastic). It has always been a great runner that fires on the first pull 90% of the time. Before this issue I can only remember it taking a third pull on a couple occasions. I've got a somewhat small yard and the mower doesn't get used all that often.

I screwed up and fed it some bad gas. The mower would start and die. i drained the tank and cleaned it out. The screen in there was iffy at best so I punched it out and installed a see through in-line filter. The carb had a little bit of scunge in the bowl so I cleaned it thoroughly, including an inspection of the needle and seat as well as holding a properly sized drill bit with my fingers to clean the jet. I then changed the oil, air filter, and plug. It got a tank of fresh gas, too.

When it all went back together it fired up and ran great for about two minutes. Then, it struggled to stay alive. At full throttle it would slow down to a weak idle before picking back up and revving to about 3/4 speed and repeating the process.

It acts like it's running out of fuel but I can see that it's getting plenty. The heat choke seems to be opening properly.

Spark seems to be a non-issue since there is no missing or smoke from incomplete burn.

What am I overlooking?