there is a manual online at www.mopedriders.org in the moped repair section for your engine. its the only batavus manual available but it covers the m48 and the m56 engines. and thats what yours has.
fuel flow on these bikes is just a gravity feed system. clean everything from the gas cap vent all the way down thru the carb. also clean out the exhaust and the exhaust piort. install a new spark plug and clean the points and she should run like new.