Just to add....
The power valve comes apart, and the valves inside the aluminium housing are brass, and usually clock up with carbon deposits. There is an aftermarket refurb kit for the valves out there though I haven't seen one for a while. Here in the UK we had the flat top carbs for about 4 years during its production period, and there isn't any spares left, I grabbed what little was left.
If I remember rightly, having good/correct fuel pressure is also key. Make sure the float is set correctly. These carbs have small fuel bowls and its good to have good fuel pressure to keep these full and refreshed with cooler fuel. Make sure your needle taper isn't worn (oval) as this means bad fuel metering.
These carbs are good, just because the boat anchor crew say so doesn't mean it is. Its only adjusting fuel, air and vacuum......