I have a Murray mower, model 309029X92. It's the kind with the Briggs & Stratton engine under the seat, and it looks like this (downloaded, not my actual mower):

I bought it sometime around 2004 and have done all of the maintenance myself.

It was running fine earlier this year, but I haven't used it in about 2 months. The gas was empty when I put it in the shed, so I filled it up with gas and tried to crank it, but it felt like the battery was weak and it wouldn't turn over.

I connected it to my car battery to jump it off (which I've done a million times), and then it turned fast but still wouldn't fire. It didn't feel like it was trying to fire, either; just spinning.

I thought maybe it wasn't getting air, so I took off the air filter for testing and it still wouldn't fire. I could see a small amount of gas in there, though, so I had probably flooded it at that point. It was getting late, so I let it sit overnight and came back to it today.

I changed the oil today, in case gas was in the oil (an old issue), but that didn't help.

I replaced the carburetor a few years ago (gas was getting into the oil), and at that time I installed a fuel valve and filter. I triple checked that the valve was on (haha), and tapping the filter didn't help. It's still pretty new so I'd be surprised if that's the problem.

I also replaced the spark plug a year or two ago, and it still looks new. By this point I was running out of daylight, though, so I'll have to work on it again tomorrow.

The mower has a safety switch under the seat so that it won't start with the hood up. It's possible that the switch is bad, but I tried shorting it and that didn't help.

My list for tomorrow is to take out the spark plug and see if it's wet; if it's dry then I guess the problem is with the carburetor. I'll probably replace the spark plug while it's out, a new one is only like $3.

Anything else you can think of that I should add to my list of things to check?