I just discovered that the Sears 28851 21HP/42" Hydro (Husqvarna Manufactured) lawn tractor has had multiple recent changes (past few months) from the electrical harness to the chassis, etc. Very notable is the change from the Tuff Torq K46-BA hydrostatic to the T2-CDBE-5X1A-18C1 transaxle...
I have never encountered this issue with any small engine.
A brand new lawn tractor with a brand new Briggs and Stratton Model 331877 21HP engine (with conventional choke), will not start with the throttle in the Choke position. However, after cranking with no start in the Choke position...