I had pondered on this topic whilst building the racer....In the end I just used the original timed breather, but enlarged the outlet pipe and ALL associated fittings to 3/8 bore, and fed it into the kickstarter cover. After the National titles a few weeks back it had put no more than a table spoon of oil/ water into the bottom, which I suck out with a piece of clear tube. There is more to the story, but it seems to work fine for me, as they said, nice round and true bores with correctly sealing rings is the answer. Cheers..........Greg.