The main thing I find in the old Twins like this is: wear in the bearing surface on the inside of the points cam itself. To solve it and make the timing [far] more stable, I shim the cam out toward the washer that retains it. In the 350 twins, for example, the points cam had [plastic] shims washers under this points cam, either 2,3, or 4, to make the gap between the end of the cam and the "end washer" .002"-.004" of clearance. While not immediately intuitive, you will find the timing to be more stable at all positions if you do this, too.
What happens is this: the inside of these points cams wears with the impact of the cam chain bumping it along, and the plastic shims get hard, crack, and vanish. Then the cam tilts a little while it starts advancing, and the advance becomes both erratic in position and "jumpy" at full advance. I make the shims from shim brass sheet, today, and you MUST use at least 2 of them, or they will lock the cam instead of freeing it to move. If you can make 3, it works even better.
Then, make sure to apply some grease to the shaft upon assembly. This helps it to even out the 'jitter' that can occur if the cam chain tensioner(s) are not taking all the slack out all the time.
What tips me off that the cam is worn inside: it is not the same timing when you insert it 180 degrees out-of-position. Thus, one side is worn a little bit...
One of the things that tended to get the cam chain adjuster bolts stripped or broken (on 160 and 175 bikes) was the attempt to tighten up the chain more than normal, to reduce this "jitter". If the shims are holding the points cam squarely against the washer face on the end of the cam, it jitters much less without this "attempt", which really doesn't help, in the end.
