Interesting carburetor on the Westbury Wombat

[Basil]

I've decided my next project is going to be the last engine that the late Mr Edgar Westbury designed. The 10cc Wombat. The carb is very different than the usual barrel type model engine unit.
After reading through the article a few times to get my head around what he was trying to accomplish here. It's very interesting and I think shows some real thought into the issue of carburetor transition from idle to full throttle. Remember this was 1968 and most model engine carburetors of this era were ultra basic in design.
Wombat carburetor,
At idle and part throttle the fuel (mixture) feed holes act as a kind of very basic emulsion tubes. Mixing the air and fuel in a ratio dependent on the sizing of the supply holes on the engine side compared to the supply holes on the intake side of the center mounted butterfly.
I find the idea certainly interesting, a little long winded with the hole sizing and all but worth a build anyway. How well it will work might be something very different but worth a try, also in keeping with his original magazine article design. Happy building

 

[Basil]

Had a good long day on the Wombat carb. Just need to add some mounting holes. I think the only change to the design I will make is to add a brass liner tube to the hole where the lower butterfly spigot locates in the body. Just for wear really as this could be a source of an air/fuel bypass leak if it becomes sloppy. Thinking of using K&S tube for this.
The machining of the butterfly was quite straight forward and not the chore I thought it might be.
I could not find any fiber washers to seal the jet assembly so used some red Delrin I had on hand. I'll need to make sure this seals adequately.
I'll start a separate page for the main Wombat build.
Cheers

 

[GreenTwin]

That is a very nice looking carb, expecially that butterfly !
.

 

[Mike Ginn]

Basil
I have looked for these engine castings and drawn a blank! Where did you get them?
Thanks in advance
Mike

 

[Basil]

Mike
I have not seen any either. I had this carb body 3D printed.

 

[Mike Ginn]

Thanks Michael - it does confirm my negative searches I guess. I'll have a look at the mags at SMEE to see the engine details but I suspect it will be a non starter so to speak!
Mike