I can't help but wonder how steep the hill is where your A has trouble. 
Anyway, there is a John Deere service bulletin that applies to late A and B carbs ( 67,71,72,73 ) in regard to the bowl vent.
The modification addesses the problem of the bowl not filling properly with fuel.
I have found the A carb, especially the DLTX-71 (gasoline) to need the modification more than the others.
My contact information is at www.popinjohn.com if you want to email or call.
Anyway, there is a John Deere service bulletin that applies to late A and B carbs ( 67,71,72,73 ) in regard to the bowl vent.
The modification addesses the problem of the bowl not filling properly with fuel.
I have found the A carb, especially the DLTX-71 (gasoline) to need the modification more than the others.
My contact information is at www.popinjohn.com if you want to email or call.