Also,

make sure they aren't stalling due to the carb flooding. The engine will be running rough and uneven. When the engine dies immediately put the trans into nuetral and hold the throttle wide open (keep your hand on the throttle because if it starts it will go wide open, so you have to pull it back quick). Try to start the engine, and if it starts get the engine speed back down. This will tell you have a rich condition,i.e. flooding. You have to turn the starter long enough to clear the excess fuel out of the intake before it will start. Be careful with backfires, keep the flame arrestor on. You will see the black exhaust smoke if it was rich.
Bill and Paul are right as usual, some other things to check.
When the carb is running on the idle circuit you shouldn't really see fuel dripping out of the venturies. Make sure the choke plate is wide open when the engine reaches running temp (if it isn't adjust it), and look down the throat of the carb(flame arrestor removed) and idle speed at around 750 RPM or less (varies a little with engine and carb type). You should not see any fuel dripping, as the idle circuit fuel is coming in below the throttle plate. Always make sure the ignition system is up to par before trying to diagnois carb problems. The carb has to have the correct intake vacum and air velocity through the venturies before they can work right. You have to have 8 good cylinders, proper cam timing and a good ignition system. What causes the carb to flood?

Idle fuel mixture not adjusted properly
High float level
Dirt in need and seat
Dirt in internal air passages
Warped mating surfaces allowing vacuum leaks, etc