The car ran OK before the work.
Runs badly after the work.
I think the mechanic made an error somewhere.

My experience is only on fuel-injected Volvos.
I've had carburetor cars in the past.

Since you are smelling fuel at the exhaust, it seems it is getting fuel OK.
Either too much fuel, or no spark (or very poor spark).

Poor work or faulty parts at the carburetor could create leaks in the carburetor - this could cause an over-rich fuel-air mixture.

Or, something was possibly damaged or assembled incorrectly on the ignition system.

If you think the mechanic is willing and able to look for errors he may have made, you could go back to him to find what went wrong.

But, since you write that he has already made several adjustments to try to get it to run properly, it might be time to visit another mechanic. If you do, be sure to give the full history of what was worked on. And ask that the work and parts (seals, spacers) be checked.

--
Sven: '89 245, IPD sways, electric rad. fan conversion, 28+ mpg - auto tranny. 850 mi/week commute. '89 245 #2 (wifemobile). '90 244 (spare, runs).