That valve almost never goes bad, just needs to be cleaned when it blocks with dirt, about once every 10 or 15 years
For the carb, it can be repaired properly, but only by someone who actually wants to repair it and actually knows how,
E.g. your fossil blocked the powervalve signal and most probably epoxied it shut too, what he didnt know that a dab of red jewellers rouge can reseat it, everything vacuum assisted on a carb is tested with a handy vacuum pump, which your guy wouldnt know what it is.
The idle, low, main and powervalve jets have air passages that help the system run properly, those are extremely important to keep free, 99% forget that and proceed to install smaller jets for (pitrol kam kardo), you can imagine those passages are a coke bottle with straw (oldschool like me) with calibrated air holes in the straw, you will need to suck quite hard with a leaking straw and a new straw will allow easy suction for the beverage.
The air passages in the carb when blocked allow the engine to suck like a fresh straw, lots of fuel all at once (black smoke, laggy acceleration, bad performance, spitting etc etc)
Tl dr
Dont let morons work on your car,