I have no idle problems with bings but my polini maxi with a 15mm bing/single reed gets the same mpg as as my 19mm delorto 4pedal maxi and the 19mm 4pedal combo is way faster to 55mph. They both have about the same top speed.
I run a dmp 70cc kit (treats kit) with a 14mm bing fast as hell but it's mpg is not so good.
I would say a bing is a good easy to tune carb that makes good power but it's sucks gas with a kit, big jet, hi performance filter and hi
Performance pipe Cause it's a rich running carb