Bang on cue comes the word from Phil Beresford at Burlen:
"It (the pin hole) is an overflow outlet to prevent fuel entering the engine in large quantities if the float chamber overflows."
Further from Phil Beresford today, comes this:
"The 289/014 is a carburetter body number from a post war carburetter used almost exclusively by BSA on their B range singles. However if the carburetters are stamped 289/014 then they may have been supplied separately as the BSA carburetters would be stamped with specification numbers on the flanges."
Thanks to "R" for the photo of his fuel level which I will be happy to copy.
In downdraught configuration the pin hole is in the side of the body so its purpose may be negated. In fact it may have to be sealed to prevent constant dribbling.
Thank you for your interest.
