Poor crop of Runner beans

Hi Folks 
My runner beans this year have grown brill & are all in or have been in flower but
hardly any beans showing  . They've been well watered & feed & there's plenty of
bees about to do there part but up to now only 3 beans  , I know there plenty
of growing time left but there doesn't appear to be any sign of a new bean growing
where the flower has dropped from, just little stalks.
Anybody else suffering with this or any thoughts why it's happening  .

Keith 

Hi again. Thanks for your reply. I forgot to say that I've used Scarlet Empress,
the same type that I've used for years, although I did mix in a white flowering
Type last year as I heard that the birds don't go for them as much but I didn't
notice much diff' so back to the old tried & tested & this year the birds haven't
Been a prob as yet. Oh bye the way I have been spraying them, like you I don't
Know if it works or not but I do it to g/house toms as well.
Keith.