Kinda sounds like your needle valves are stickin in the open position. These daul-jets are the worst part of the 3.8. It is also the crappiest carb known to man. I'm suprised it lasted this long.
You can try rebuilding it, but I would look into another kind of carb, can't help you on what to put on it, but i would look into it though.
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'69 G.M.C. Short/Fleet. 350/350 Trying to clean up the left over damage from the
Dope-Smokin-Old-Man http://geocities.com/andys_69_gmc/
I've been dubbed the Longhorn
Freak/Fanatic/Expert, I just hope I can live up to it.
Should be getting theone ton Longhorn with a
PONTIAC 350/350 THIS WEEKEND!!!! thanks every one! 
Visit
The Longhorn Site http://geocities.com/MotorCity/Flats/8752/
If you need a pic posted, e-mail me at
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Andy, in Columbus Ohio