That place kind of sounds like the place where my parents took our 460 powered jet boat and wouldn't you know it, the poor thing had asthma after they "fixed" it.
they put a little *650cfm carburetor on it. Took it to another reputable shop and they actually fixed it with a 850 double pumper.
The poor thing used to buzz up to 5500, and after it got leaned out so much from that tiny carb, it completely ruined that engine. it struggles to rev past 4500 now. :(
*my dad just reminded me, the crappy shop charged for an 850.