It's a good idea, but not required
My read of the text, and Chapter 11, is that while it's not a hard and fast requirement, it's another good method to reduce risk in flight.
"e. Fuel Flow and Unusable Fuel Check: This is a field test to ensure the aircraft engine will get enough fuel to run properly, even if the aircraft is
in a steep climb or stall attitude.
(1) First, place the aircraft?s nose at an angle 5 degrees above the
highest anticipated climb angle. The easiest and safest way to do this
with a conventional gear aircraft is to dig a hole and place the aircraft?s
tail in it. For a nose gear aircraft, build a ramp to raise the nose gear to
the proper angle.
(2) Make sure the aircraft is tied-down and chocked. With minimum fuel
in the tanks, disconnect the fuel line to carburetor. The fuel flow with
a gravity flow system should be 150 percent of the fuel consumption
of the engine at full throttle. With a fuel system that is pressurized,
the fuel flow should be at least 125 percent. When the fuel stops
flowing, the remaining fuel is the ??unusable fuel?? quantity.
(3) Since the fuel consumption of most modern engines is approximately
.55 pounds per brake horsepower per hour for a 100 horsepower
engine, the test fuel flow should be 82.5 pounds (13.7 gallons)
per hour for gravity feed, or 68.75 pounds (11.5 gallons) per
hour for a pressurized system. The pounds per hour divided by 60
equals 1.4 pounds and 1.15 pounds per minute fuel rate respectively.
NOTE: Formula for fuel flow rate gravity feed is .55 x engine
horsepower x 1.50 = pounds of fuel per hour divided by 60 to
get pounds per minute, divided by 6 to get gallons per minute. For
a pressurized system, substitute 1.25 for 1.50 to determine fuel flow rate."