Richard, the Walbro in question isn't a butterfly carb but a barrel throttle. Walbro has a couple series that use this arrangement. The WZ series is the best of the two series for planes as it has an adjustable top end. The WY series has a fixed top end that can only be adjusted by a carb tear down and an orifice replacement.

The WA and WT series are the ones most used for Aircraft engine carbs and while I like the looks of the WZ, the throttle return spring is a major issue along with the barrel ramp which is cast into the housing and the throttle arm follows. The arrangement is going to need a lot of modification to work, so the WA and WT are the most likely for use on a plane engine.

Downunder, you bring up some interesting ideas. I have a Saito 150 that I'm converting to ignition and was looking at a carb for gas. I've been told that it will run on gas with the stock carb, but the mid range is tricky. Perhaps a bit playing with the spray bar may cure that.

Good stuff guys, keep it coming.

Don