If it will not idle longer than 5 to 10 seconds, it is the Low Speed Needle.  Use the pinch test, that is, make a high speed run, stop the car and immediately pinch the fuel line close to the carb.  It should idle up for about 3 seconds then die.  If it takes longer than three seconds, then the LSN is set too rich and you will need to lean it about 1/8 of a turn.  If it dies right away, then the LSN is set too lean and you need to richen it 1/8 of a turn.  After each adjustment make a high speed run to clear any extra fuel out of the car and do the pinch test again until it gets set right.