You must first realize that adjusting the low end affects the hi end on a magnum! So anytime you adjust the low end, back off the hi end and readjust it. then look for the hesitation. This stall can be from either a too rich or a too lean state. Its really hard to tell. 1st question is: how much have you turned in your low end? What type plug? What fuel?
Magnums like castor! 10-15%... Iwould probably stick with 10%. Try an OS #8 or a K&B 1L. If you turned the low end needle in alot then back it off 3-4 turns and start over using the above method in 1/8-1/4 turn increments. If you have'nt turned the low end needle much then continue w/leaning the low end as mentioned above. Also how much fuel has been run through the motor. You need to run at least 3 tanks through it at 3500-4500rpm before you ever try to adjust idle.