thanks folks, it is a euro spec '89 model. don't know if its a keihin carb but it looks very similar.
the top tube is only about 6" long smaller diameter than the fuel line. the drain tube is about the sam size as the fuel line
The good news is i got the bike to start at the weekend, ran for a few minutes, i left the smaller top tube end unconnected.
I still have a bit to do, didn't sound to smooth, so no doubt i'll be posting some more questions....