71 340 running bad

71 TQ is very different from 72 up. No wells to leak, no o-rings to seal the primary jets. Might be time to pull the top off the TQ to check float levels, jet sizes, rod numbers, and such. What cam are you running? Did you find true TDC? Did you centerline the cam? What compression are you getting? Get a vacuum gage. New factory engine means nothing, I could tell you stories. Who did the heads?