I have a similar issue with my '76 (weber 32/36). It is slow to start when warm and there is a gasoline smell (no visible leaks). I searched and found this thread,
Thread Topic: Flooding and Hot Start
http://www.bmw2002faq.com/component/option,com_forum/Itemid,57/page,viewtopic/t,361719/highlight,fuel+filter+bypass+valve+fuel+return+line/
It sounds like the "filter fix" you are describing.