before you start messing with the carbs the timing/ignition and valve clearance should be dead on. I agree with the other poster, new cap and rotor, also consider new S plug wires. You alos need to check for the dwell on the contact points when you do the timing. Poor dwell on a worn distributor will cause various unhappy symptoms. Which brings me to the final point, some of these ol dizzies are just too sloppy to give you a decent reliable spark for more than 40 hrs or so on a brand new cap and rotor, there is too much play in the shaft to set up consistent dwell, and the wobbling shaft also wear out the cap and rotor prematurely.