Volkswagen Golf fuel

my car has fuel in it but sometimes when im driving the gauge drops and then the car stops as tho its got no fuel. when ive gone out to start it in the morning sometimes it will not start and the gauge is fine but when i turn the key to start it up i just give a puff of smoke from the drivers side and it smell of fuel. ive had new leads and distributor cap because the garage thought it was cutting out everytime it was wet conditions. but i know thats not why this is happening. please can anyone help cos now i dont like driving the car just in case it cuts out even tho ive got fuel.