If it's retarded, as in all the way ccw. It could be your timing chain is worn.
As the chain wears, it gets longer. This extra length between the sprockets on the front side lets the cam be retarded. If the cam is retarded the timing will be too.
One way to easily check for can chain wear is to put the timing marks at TDC and look at the pin the copper cap rests on. It should point straight up or down.
As you look at that end of the cam, the more the pin is toward the rear, the more the timing chain is worn.
On my 75 my chain was worn enough so I had to set my timing as you are doing. With the points plate I even filed the area under the screws so I could go farther.
It ran ok but not as well as it did with a new chain.
Leo