[Da_Bian]

dont know what car you have, but if its not efi then...

i've had the exact same problem
turned out to be the fuel solenoid
its basically a switch/valve that is directly plugged into your carb
its duty is to supply the carb with fuel
sounds like its failing and is cutting the fuel off occasionally

its cheap as chips to replace. you could do it yourself if you wanted to. but i'd take it to a mechanic if i were you.