A Walbro with a "28" or "27" cast into the venturi would be ideal These are basically &/16" venturi carbs.
The most popular number for this size carb is WA167-1
But there are many more.
There is a list on here if you look down a ways.
If not, I can PM one to you.
Here's alink to the list....
http://www.rcuniverse.com/forum/m_3811393/tm.htm
Enjoy,
Jim