just my .02...
Honda's have a vaccuum operated fuel pump which is why they can draw fuel from an external fuel tank as long as there are no air leaks between the external tank and the cap on the honda.
Yamaha and the Champions don't have the fuel pump built in. I've seen a few mods where people have purchased the fuel pump and put it into their Yamahas and Champions and external tanks work the same as the Honda.
There are a host of threads that outline how to create your own external tank. Most, do, require the external bulb to prime all the air out of the line.
Josh