Actually the ignition switch can cause the engine to buck and stall much like you have described, you don't need to replace the tumbler, just the switch portion. To be sure about the problem, attach a test light to the main outgoing feed wire to see if the power quits while the engine stalls. I have attached a diagram.
Please let me know how it goes,
Sunday, October 25th, 2015 AT 4:03 PM