Car surges

[67mopar]

Hi all
67 chrysler 383 seems to "surge" at about 60 MPH. two barrel carb rebuilt, 383 rebuilt car runs very nice. It seems to have a lot of power, just surges when you maintain a steady 60 or so miles per hour.
could this be the floats or accelerator pump?
Thanks

 

[Welder guy]

Check the fuel filter , it may be getting plugged up . It a cheap and easy first step.

 

[CBODY67]

Not floats and certainly not accel pump or idle mixture adjustments. Might be a broken diaphram in the vac advance, though. Fuel filter is a good place to start, too. Ign timing and dwell?