flat head carb

Put a stock gas jet in it.

No, it won't be perfect, but it will run just fine (depending on what your purpose and application are.)
I do not use a big offset throttle shaft when building a gas class flathead engine. IF your engine has an offset shaft, you'll likely be down real low on the needle setting on gas with the stock gas (34) jet. Start the needle setting at 3/4 of a turn out and adjust from there.

Thanks and God bless,
Brian Carlson
Carlson Racing Engines
Vector Chassis
Vector Cuts
(25 years full time serving the karting industry)
215 N. High St.
Linden, IN 47955