I have a 72 gmc pickup with a 350engine and a 4brl carb,the problem is that my carb is not getting any fuel but when I remove the fuel line from the carb it's full of fuel,and when it does run as I step on the gas it just bogs out,also while engine is off as I press the throttle I can see a strong stream of fuel coming out the jets.but when running no fuel comes out of the jets at all

I don't know the vehicle, but the carb bowl is not venting.

Could be charcoal canister system, bowl vent etc.

If you loosen the gas cap it may improve. That isn't a permanent fix.

I don't know the vehicle, but the carb bowl is not venting.

Could be charcoal canister system, bowl vent etc.

If you loosen the gas cap it may improve. That isn't a permanent fix.

While the engine is off fuel comes out the jets just fine but while running it won't

It sounds like you need that carb overhauled and cleaned in an ultra-sonic bath to clear the tiny passages that have likely become varnished over time.

When you step on the gas, the accelerator pumps gives a visible squirt of fuel to provide power, but when the engine is running at idle, little fuel is needed and often cannot be seen.

Find a shop that specializes in carburator work and have them check yours. Once finished, you should have plenty of power and performance.