engine bogs down

Whats the carb number? Has the carb been modified? Have the counterweights for the air valve been lightened? Is the float level correct? What hole is the pump rod in? What are the jets, rods and springs? Is your PCV system set up right? Does your vacuum advance diaphragm leak? What is your vacuum at idle?

There are lots of things that would be helpful to know. If the carb has been "tuned" (monkeyed with) I would say thats probably your problem. But not knowing where you are now it's hard to know what to suggest.