excitement screaming on leash when he sees another dog

We are struggling with Kernal he is 18 months old was 5 months when we bought him he had not been socialized, he is perfect in every way apart from outside on his lead screaming and shouting for other dogs we have tried even a police dog training, whistles, water, clickers, toys collars nothing has worked it is very frustrating we have bought another Milo whom Kernal adores they love each other but it still has made no difference to Kernal's behaviour outside