strang idle/stalling when cold

Hey guys my dad has a 89 pick up with the 22r motor it is carbed
when you start it when its cold you have to pump the gas to get it to start
then the idle will go up and down untill the engine has reached its normal running temp. but when the idle is jumping it it will stall after about 20-30 seconds
when its realy warm it runs like theres nothing wrong
any idea what could be wrong
thanks for all the help