Handsome bike indeed
If the AR10-501 Gurtner is gone then the carb has already been 'upgraded' to a carb that is not so sad and weepy. If you feel the performance is a bit lacking check if the 'new' carb is bigger than 10mm and that the intake manifold is bigger than 10mm ID. Some of the AV7 came with larger intakes than 10mm but for the most part if Motobecane originally fitted a 10mm Gurtner on there the intake is matching ID.
The AV79 was issued as a 40km/h rated bike (25mph) and is capable of a lot better with just an improvement in breathing but upgrading to a 15mm carb and intake as well as derestricting the exhause and setting the ignition timing at 1,5mm BTDC.
Check that the brakes are in good order for the speed improvement, should have the 3rd model Prior Monobloc brakes which are capable of stopping the bike from a bit higher than 50km/h (30mph).