There are many threads with the same problem as your's.
I don't know why its always the power valve being bad which may be 1 out of a 1000 being bad, and very easy to tell if it is bad.
If you expect a blown power valve, use this simple test.
TEST: At idle turn your idle mixture screws all the way in.
If your engine dies the power valve is not blown.
95% of the time a bad power valve will cause the carb to flood out and can be seen from the top of the carb, you will know something is wrong thru the whole RPM range.
for a stumble , Jetting & or a larger squirter is called for.
What are the color of the spark plugs ?
Adjust the floats to the very bottom of the sight plug, the clear sight plugs can be deceiving, I like to adjust the floats with the plug out and the gas just barely trickles out when rocking the car.
Sometimes the intake gasket moves a little and leaks to the other chamber from over tightening or using silicone sealer which would cause it to hesitate or backfire.
My .02 cents worth is the float level is high.
Luv the smell of NITRO in the morning.