I just bought this used mower, DYT 4000, Craftsman. Mowed my yard for 20 minutes, then the motor started 'missing'. It acted as if it had two cylinders, and one wasn't firing, but it only has one cylinder. The rpm's stuttered with a rhythm, as opposed to the rpm's surging, higher then lower. New plug, gas, filters, as of this weekend. I let the mower sit for 20 minutes, then mowed 10 more minutes, and it started again.
Here's the number from the motor: 31p377-0348-e1

Thanks for any help you can give me.

Did it die , or just bog way down ?

Thank you very much for looking at this message.
Didn't die, it just boggged way down. I disengaged the blades, and that didn't help the issue. I drove it across the yard and to the garage, moving the transmission to higher and lower gears, and the issue didn't change. I gave it more, and less throttle, and the issue didn't change. Then parked it. I pulled the spark plug, and it was white. Replaced spark plug.

Sounds fuel related for sure.
Check the fuel cap first . Sounds like it might not be venting.
Luck

Mowing today or tomorrow and will let you know. Thank you so much for the help.

Got to mow yesterday, works fine, you're a genius! The cap has an air filter in it, and a small hole in the outside/middle. I ran a small wire into the hole and it was clogged. Now it mows perfectly. Thank you thank you! Saved me a ton of time and money! Have a great Summer, hope your mower runs as well as mine. :)

Your welcome glad it worked...