At 2500ft OEM jetting should be fine. It's extremely lean out of the box at sea level, as you go up it comes closer to ideal but I'd venture a guess you could still use another 1/2 turn or so on the idle screw (hidden under a plug on the bottom of the carb). But that wouldn't be causing the problem you have. After it stalls, the plug is soaking wet? Opening the throttle delivers more air, not fuel, so when an engine craps out blipping the throttle it's more often that it's too lean, and the extra air kills it.
The only thing that comes to mind if the choke floods it out is the little rubber plug that restricts what the choke circuit can draw (if you pop the bowl off, there's three tubes extending down into the bowl. One holds the pilot jet, one holds the main and jet nozzle, and the third should have a rubber stopper in it. If that stopper is leaking/missing/fell out (rare, but have seen it), the choke will draw waaaay too much fuel up and rather than give a rich fast idle, flood the engine out almost instantly.
I'd pop the carb off (not difficult) and have a peek around the bowl. Check that rubber stopper is in place and snug. After 15 years, carb could probably do with a cleaning.