xs1100 carbs flooding?

i have a 1979 xs1100.the carbs have been stripped and cleaned.the jets,needles,float valves and housing,gasket etc have all been replaced.the tangs on the floats have all been lightly cleaned up to rid any wear.the floats were tested for leaks,all ok.the float heights are all set as yamaha manual to26mm. if the carbs are tilted with bowls off it looks like all the valves are working and are closing.each valve has its own filter so no dirt is present.when the carbs are fuelled up petrol fills the bowls then runs out of main air jet at the rear of each carb.they have been removed several times and checked,no fault found.in the past what ive done usually does the trick on other bikes but not this time.can anyone out there help.thanks,