Since you have it apart already, put a new gasket set in it. Replace the base to manifold gasket, too. Might also want to check the carb isolator for cracks. Other places to look for leaks are the manifold to head gaskets and the wiper vacuum supply hose, if equipped.
Another thing to check, just judging from the description of what it's doing, check the timing. You may need to advance it a bit.
