thanks for the reply. i have downloaded it but simply not found the relevant info at first glance (seems to be a phenomenon of the digital area: lack of patience ..).
after browsing through the doc 2nd time i have found info on page 51.
@rob: thanks a lot for the info about the amal carb.
thanks for your feedback. meanwhile i have readjusted the carb according to the data provided by rob. now it runs quite well but does not have a stable idle. when stopping at red lights i have to twist the throttle to keep the eninge running.