If the 500/550 engine has too much advance, it falls flat on its face until about 4500 RPM. That's one good clue...
The Dyna S ignitions have a [long] history of being somewhat temperature-sensitive. The gap distance between the magnet pole in the cam and the pickup(s) on the plate must be very close to the Dyna spec, or it will be affected in 2 ways:
1. It will act very cold-blooded when starting.
2. It will tend to "hang" at above-normal spark advance, due to poor turn-on, when hot.
Most of the time, the gap is too big when these symptoms occur, so check the distances on yours, and make sure they are identical for both the left and right side.
Another problem they have: sometimes they sent the wrong advancer cam out with the package. The hole in the center of the cam is too big on these, and it lets the cam wobble. When it does, it tends to mechanically "stick" when decelerating from full advance, which also makes the engine "hang" at high RPM. Make sure yours isn't "wobbly" on the spark advancer?