1. Would a set of Boysen 607 Power Reeds help?
They will improve throttle response, but won't fix an existing problem (well, unless the problem is bad reeds ;) )
2. Could I cut it back to 40:1?
Yes. Unlikely you would ever run your bike hard enough to 'need' 32:1. Keep in mind that changing TO 40:1 is a change to the rich side from 32:1. That is going to make a jetting issue worse.
...which is likely the problem.
Check:
http:/justkdx.dirtrider.net
1997 to 2001 KDX220
With a performance pipe/expansion chamber, air box mods , the factory or after-market silencer and the stock 33mm carburetor run a 42 pilot, the stock R1173L jet needle in the second from the top clip position, a 145/148 main jet and fine tune the pilot circuit using the air screw.
the jetset you're running is closer to a 200 setup.
All circuits pretty much effect all other circuits. A too fat main will easily mess up the pilot/AS circuit. Chances are you're WAY rich on the main.
I say 'chances are' cuz each bike/rider is different. Only YOU can do it up right.
Still...jetsets on particular bikes are USUALLY close.
The only way (well, excepting fancy A/F ratio devices plugged into your exhaust) to check the main is a WOT plug chop test on a new plug.
After that is set, set your pilot/AS on throttle response, or 'seat-of-your-pants' results.
The kdx can and should snap immediately on an off-idle to 1/2 throttle quick-wick. With a 220, you should have trouble keeping the front end on the ground doing that!
Why a 14T CSS? With a 50? You're kinda going opposite directions on the two sprockets. That's not helping bottom end response issues.
If this is a 'new to you' bike, there are other possibilites...like no compression in the motor. Don't fret the big stuff 'til you fix the small stuff. (imo)
BTW...13 on the front is OEM (13/47). Again...why 14/50? That's higher than stock (47/13=3.61 vs: 50/14=3.57). That's not generally the direction riders wanna go.