Hmmn, could be an intake manifold leak? That would do it, I reckon, how hard did it get leaned on during the carby changes? Some suggest testing this by using an oil can to place a bead of oil around the manifold gasket to watch for air bubbles, but I never found that worked well, and you cant see the bottom half of the intake manifold anyway. If you have a manifold vac guage you can diagnose it, but if not, check all nuts to the head are good and tight for starters.
Consider replaceing the manifold gasket, if you do so, make sure to totally clean the mounting surfaces on both manifolds and the head to schmicko with a scrape, then a handheld grindstone before fitting the new gasket. (Hope I am not patronising anyone here, either you know or you dont!).

If not intake manifold, then pehaps you've inadvertantly caused something else to change whilst fitting, refitting the carbs, but what... its always the question, did someone push on something too hard, not do something up right, are all the varijet hoses back in their original positions..etc

Maybe firstly, start from scratch, check electical basics; alternator connections, ground connections, coil connections; then basic fuel system, pump, hoses etc, then the carby jets. A quite common thing to happen is for a grain sized bit of rubber to come off the inside of the fuel line when refitting the carb, getting into the works and then blocking a jet that was previously working fine. If no luck, have a look at the manifold gasket, its another 10 -16 bucks.

Oh and P.S. hitting it with a sledge hammer probably will not help, sledge hammer usually bounces back off and breaks left shoulder blade.... engine behaves the same. LOL lol.
Cheers, Dave.