RESOLVED (at least 95%)
I want to make sure folks understand some Downtowns have this problem, some don't No, it is not as simple as a faulty spark plug wire, or replacing roller weights, or any other minor defect. It has to do with the mapping of "some D/T's" of the fuel injection during the process of acceleration in relation to throttle position.
D/T owner "enslin" who posted on the same topic in another thread messaged me back that they received a new computer from KYMCO under warranty and apparently that resolved it. However, below is a hint how to minimize the surging/hesitation/flat spot characteristics.
I do not have the time today to write a long essay, but in principal the British fellow "jimmyuk" I quoted above is right, the MAP sensor position makes a huge difference. On top of that, the TPS sensor position has also an influence.
After about 6 hrs of extensive adjusting and on-road "testing" I have found (at least for this D/T) a setting that works very well, MUCH BETTER than it was, about 95% perfect, and very tolerable now.
You can find pictures on-line of the MAP sensor e.g. in the service manual, it sits right atop the air intake assembly with a metal locking tab and one Phillips screw. In the first step turn the MAP sensor around in small increments while the engine is running until you reach the highest idle rpm. My best position is about 11o'clock of the wires coming into the MAP sensor (looking from the left side of the scooter into the engine compartment), different from 1-o'clock where it was originally. Eventually the computer will lower the high rpm to an acceptable idle rpm. Take it for a test ride (just pop the seat on the scooter to make it easy) and try. Test different positions of the MAP and make notes or pictures what you feel so you can go back. This should make a noticeable difference already.
If it is getting better but not enough, the next step is to go to the richer side of the setting of the TPS, still in factory specs. But that is another chapter...
