Mechanical fuel pump pressure may be adjusted by changing the tension on the diaphragm spring. An incorrect spring can create too much (or too little) pressure.

Testing will confirm/deny that the pressure is OK.

The carburetor is supposed to be rebuilt. Just giving some respect (possibly unjustly) to the rebuilder. Hopefully he/she knew what he/she was doing.

Jon

Good carburetion is fuelish hot air
The most expensive carburetor is the wrong one you attempt to modify.
If you truly believe "one size fits all," try walking a mile in your spouse's shoes!
The Carburetor Shop