Hey Dougt I have an old kiortz with points ignition and it had about the same size ventury as what you discribed. I open the ventury with my rotary toll and man did it make a difference. I ended up putting that carb on my 25 cc homelite and got 14lb of thrust with a 18-8 wood prop at 7200 rpms.
So go for it and see what you can get, open it to about 3/8 and try to keep the metal out of the pump section.