Re: 1979 CB650 Carb Parts for Sale
From what I picked up here, seat problems seem no known issue for the PD carbs.
The many leaky carbs threads (for both types) typically just result from debris in the tank.
That's why we always write: clean out your tank!
Another option for leakage may be mixing up parts from different carbs.
Especially the floater cams are susceptible to small damages.
One possibility to check out the success of valve seat polishing is to blow into the fuel line with the carbs upside down. Then the blow should be blocked and also you should see no bubbles when you put a bit of fuel around the valve seat.
BTW, I think for the PD carbs it is possible in principle to mount the floats upside down. No idea if this will cause seat/leak problems however. Nevertheless this is how they should be: