I had a similar problem once on a '68 Volvo 122. Best car ever made by the way. Anyway, I tried all the usual steps like making sure fuel was getting to the carburetor and spark was getting to the plugs. Went through a whole 6-pack of Pabst Blue Ribbon trying to figure this problem. I figured I must have broken a timing gear or something like that. Took the front timimg gear cover off and found that everthing looked great. Finally, after a couple more ice cold PBR's I was looking at the points again and noticed that the distributor was sticky. When I grabbed the rotor and twisted the shaft I could feel it sticking. Replaced the distributor and the car has been running like a sewing machine ever since. What was happening was the distributor was not setting the rotor at the correct point because the shaft was hanging on a burr or worn groove or something like that.
