For a First 235, replace the CDI with a Schaefer SnapFurl.
I have seen that CDI can't adjust luff tension very much, because it is dependent on the compression rigidity of the foil. A friend bought a boat with a CDI furler, and the foil had a couple kinks in it, so it wasn't completely straight. Trying to get more luff tension would just bend the foil some.
The Schaefer uses the existing halyard to hoist the sail, and thus offers much more control of luff tension. That's important for winning!
I wouldn't have recommended changing furlers for my friend's old boat, because it was a Com-Pac 19, and it wasn't going to win any races for sure!