Junk in the tank can cause that via fuel starvation.
Back in the 80's I had a '65 GMC with the big V-6. Rust in the tank would flake off and get stuck right where it entered the carb (someone took the filter out - fortunately, Dad had an unused stone fuel filter that fit the Stromberg). The flake was hard to see, Needed needle point tweezers to get it out. Could see through the flake, it was that thin.
JohnBAdams - If you throw the tranny into neutral and give it some gas, does the engine stay running? That's what I had to do until I could get the rust flake out of the carb. Pain in the freakin' @$$.
Dean