318 V8 running sickly

Hey Guys,

I have a few questions and hopefully someone has run into this problem - last week I started my dart and it was running excellently. I pulled it out of the garage and let it sit running to warm it up. As it was running all of a sudden it started to stumble really bad. I thought it might be out of gas so I turned it off and put fresh gas in it. Now it will hardly run - barely starts - it's getting gas - it's getting spark - but can't figure out what would have made it start running so terribly - installed a new gas filter on it and no difference. The car has a Autolite rebuilt carb ( 2nd one in 5 years) and was wondering it that could be the problem......... it originally had a Carter carb and I still have it.
Does anyone have any idea's why all of a sudden it would go from running perfect to barely running? it's has a new gas tank, fuel lines, fuel pump etc....... everything is new that bolts on this engine........ I am just stumped.
Also, does anyone have any thoughts on Carter carbs - good or bad?
I'm thinking it's a problem with this Autolite carb again - it's a rebuilt one from Rockauto ....

thank you guys !