hard miss and popping at low speed

[snappercutter]

12.5 briggs on craftmans rider. runs good at full speed but has a miss at low speed. 10 year old motor but is basically new. mower looks brand new and was seldom used

 

[bertsmobile1]

pull the blower housing off & check for nest debris.
If am interperting you properly it sounds very much like the inlet valve seat coming loose. .