Yeah,I figured that.If its flowing out the back of the carb or into the exhaust,the float should be stopping it. (On my bike,the other (3) carbs are fine. I set the float heights,cleaned the carbs and everythings been rejetted, balanced and run on the dyno.There are no overflow pipes (BS34s). I even cleaned the offending carb again.)
My way of looking at it is to start at the beginning,which is the tank.If thats dirty,theres no point cleaning out the carbs or the petcock as theyll just get buggered up again. Is your tank clean Edward?
Then look at the petcock. Do you have a vacuum tap or the other sort? Is the tank filter clean? Im busy rebuilding mine. Scirocco dug up this link for me.Its very useful for rebuilding vacuum taps;
xjbikes.com/forums/threads/rebuilding-th...-valve-w-pics.25058/
(After that,Ill clean my leaky carb again and have a closer look at the float mechanism)
If you do get the tank and the tap clean,it might be worth putting an inline filter twixt tap and carbs.Just to be sure.