Problem starting 71

[dragonlord2167]

Hi there new here and have learned a lot from reading thru the post and thank you for it but I'm truly dumb founded I have a 71 chevy with a 350 four bolt main its a brand new crate engine and i just installed it I put everything on her brand new except the distribuator its HEI but it has a new 650 edelbrock carb new alum intake new fuel pump like i said everything is new what my problem is in the morning or after it sits a while it fires up great but after driving around and when I shut it off and go to start it all it does is turn over unless I put it to the floor and she will start checked all vacuum hoses can't find a leak but when its running it seems to be running ok except when I stop at a light it wants to die down sometimes I tried to turn in and adjust mixture screws and they don't do anything for her it doesn't change anything so I'm hoping someone here might be able to give me some pointers and maybe help out.