The carburetor is a high maintenance item, that is one reason all car makers now use fuel injection.
No way to tell what is wrong with your setup, but most likely it just needs to be repaired back to factory specs.
There are very few mechanics working today that are skilled at carburetor maintenance. In your case, a complete inspection of the engine is called for.
Start with a compression check.
Check that the computer controls are all installed and functioning properly.
Check for vacuum leaks on intake, carb, and vacuum system.
Check slack in timing chain. Much over 6 degrees calls for new timing chain and gears.
Check for last known tuneup, if unknown , do a complete tuneup including filters.
If carb will not adjust, overhaul it or replace with new. In Ca, you are limited to OEM carb or fuel injection upgrade.
You may have something minor, or it may need a lot of work, only a real inspection will tell you.
Expect to pay $500 or more for a detailed inspection and tune up, labor is very expensive, and most folks here do their own.
418 miles on 19 gallons of gas. Can't beat the BBD !