When I installed a new Bocar 34-3 carb on my car, it was plagued with a number of problems that caused poor idling/running.
Probably not what you would want to do with a new carb, but if the other suggestions don't yield an improvement, I would remove & rebuild (yes!) the new carb. Mine had a lot of what I guess was casting debris (fine sand?) in the fuel bowl. Buy a couple large cans of gumout carb cleaner and act like this new carb is 20 years old - completely disasssemble and clean thouroughly.
Buy a good quality rebuild kit and use everything that fits (the bocar gaskets are awful and on mine you could actually see seepage from the cover down the bowl side). The bocar o-rings for the 2 adjustment screws were already cracking when I removed them, even though the carb was only about 1 month old.
Also buy a good carb to manifold gasket. The one that came with mine was way too thin & flimsy. I bought 5 good ones from Rocky Mt., keeping the extras as spares.
Also, use JB weld, muffler cement or silicone on all the casting plugs to prevent either air or fuel leakage.
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