Poor throttle response - Tuning advice needed!

#1
My 10HP briggs with mystery Walboro carb ($5.00 carb from ebay, bolted right up) has TERRIBLE throttle response just off idle.

Adjusting the air screw makes an improvement, but I am not satisfied with the result.

Here is my evaluation:

Idle is fine.
Any throttle between idle and about 1/8 throttle wants to die, no power.
Midrange is fine, once she clears out.
Top end if fine, for the short amount of time I can hold it open, my street is only 1/10 mile long.

If this were a "real" motorcycle, I would begin the process of changing the pilot jet.

How tunable are these carbs?

Am I wasting my time, is this just the nature of a big-bore flat head engine with a low-tech carb?

Is a Mikuni the way to go?

By the way, the governor is gone... My twist throttle move the butterfly directly.
 
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