Help!!!!

My guess is points. You need a dwell meter to make sure the gap is set right, after installing. Per the '66 FSM 28-32 degrees dwell is needed. Point gap is .014 to .019 ". Setting points is sometimes a matter of trial and error depending on your skill. Its easier to set them with the distributor pulled shoot for the mid range of the measurement, something like .017". Make sure to install the dist in the same spot with the rotor pointing in the same direction as well. If your motor is stock, then an initial timing setting of around 10 BTDC should be a good starting point. Remember to put a thin film of dist grease on the rotor and rubbing block, do not get the points greasy.

You might also check your vacuum advance to see if it is leaking. Put a length of hose on the adv nipple and suck on it with your mouth. Hold your tongue over the tubing in your mouth and see if the vacuum dissipates - watch the arm on the vac adv unit inside the dist to see if it falls back relatively fast. If so, its bad. If it holds vacuum, its good.

Let us know how it works out for you !