I just purchased my 1966 coupe last year. Got a tune-up a year ago. Was running smooth. Now, however, it runs rough. What to do? Started looking at web pages that describe do it yourself tuning - way to technical. Terms I don't know the meaning of.

Could be rust in the gas tank, timing, carb . . .

Seems to be roughest at idle. Notice it at low speeds. When I get to 30MPH don't seem to see a problem. It has inconsistant roughness. Sometimes smooth then it noticably skips (misfire?).

 

if the diustributor is still original you might be running points as a spark breaker.
So get rid of the distributor cap and see if there is a breaker point. a little contact with a leaf spring. If yes, this needs to be adjusted or replaced. There must be a few articles on how to do that. Once that is done see if you need to replace the distributor rotor and cap, plugs or wires. Once that is sorted or if they are all ok adjust ignition and carb.
No matter what you do check on the breaker first. every few 1000 miles that thing needs adjusting.
it's hard to tell what's wrong with your car, but that would be something I'd check

 

Check your timing also.

 

Idle mixture, could be lean or too rich. Try turning the screw at the bottom of the carb facing the firewall, thats the idle mixture screw, if that doesn't do it, then it is probally one of the previously mentioned problems, good luck!

 

if its just at idle your timing may be off, id check that first

 

x5 for timing. When I bought mine it was pretty rough at low speeds <30. I thought it might be the carb but turned out the timing was just way off.