Usually means that you LSN is a little rich. Does it rev up a little before stall, or is it immediate?

Will it idle good for 30 secs? (I know I have a problem not blasting the throttle for that long too!)

Usually if a car revs up while sitting at idle it is too lean, if it just shuts off after a while at idle it is too rich.

You should be able to sit at idle for a good 45 secs to a minute with out any probs.



As far as the mixture changing on you, could be the fuel, or at the most you might need new O-Rings for the needles, but I doubt that.
HTH
Anty