In particular a Briggs & Stratton 20hp. It will run fine for a while & then start stuttering. After that it'll only run on full choke & after a while it won't run worth crap at all. Sometimes the next day it will crank & run fine. Other times it still acts up. It's a mower so it kind of gets irritating when you get half of the yard cut & have to cut the other half the next day or later in the week.