For good midrange, the pipes need to be 10" long (25cm) when combined with MTW td75K mufflers. With TD75, the headers can be 1" shorter
I tuned the carb on a DA100 when at MTW, and had the engine carb set up in about 5 minutes with excellent response at all throttle settings. For carb tuning, see
http://www.prme.nl/forum/viewtopic.php?t=54