Unfortunately, like most of us, I believe he changed the fuel filter after he started having problems instead of when he installed the new carb.

Also, check for a vacuum leak, a vacuum leak can cause this type of problem too (vac gauge will tell you). The choke will compensate for the increased air until the choke opens, at which point the metering rods won’t operate correctly because of the low vacuum.

And, if you have an automatic transmission check the vacuum line connection at the transmission to see if it has come off or burned against the exhaust (often overlooked).