1996 Nissan 240SX stalls when warmed up

1996 Nissan 240SX mileage: 134,000. We are currently here in South Korea and it is very impossible to find a good mechanic that understands our car problem (not Korean made). We recently changed the spark plugs and distributor caps. When we start our car in the morning, we don't have any problem starting the engine. But when we drive it for about fifteen minutes, it will stall and die and it won't start. It will start running again if we wait for at least three or more hours.