Firstly congratulations on the Beat!

I'd go down the list of usual suspects, starting with the easiest first. Note that revving it might be masking some misfire throughout the rev range:
Give it a good run, it might just be some iffy fuel that needs cleaning
Clean inside of dizzy cap and check for cracking, and check the rotor (and its cleanliness)
Clean HT cables
Replace spark plugs (they are cheap enough)
Check air filter (you never know, it could be blocked)
Check and clean out the air control valve
Replace the fuel
Replace ECU caps

The dizzy being replaced was due to it seizing because of poor oil supply, so it is either completely broken or not.

Hope this helps!

Stu