1 1/2 qt of fuel ?? wow that's a lot of fuel!

Note a 6x3 at 18k static is producing very good power.
17.6oz thrust / .154hp / 115w

Did you plug in the back plate pressure line into the tank to put pressure on the bladder?

You have ran a ton of fuel through the engine it only needed 6oz of fuel to break it in.
Since all this has been static the ball socket has been stressed with a 6x3 prop.
Odds are very good you have a loose socket now and need a reset tool to fix.
You will need to check this before running any further. Always bench test with less
prop to keep the load off the ball socket and keep it a tad rich for further compensation.

Only brief peak settings for quick power / rpm check on the bench.

You can take the NV body off the carb body remove the NV put fuel line on the nipple
and flood fuel through to blow out any possible hairs, silicon or any foreign materials
that may have gotten at the feed hold to the venturi.

If the Venturi was found loos this would for sure reduce suction and the NV would end
up out far to compensate.

I always pull the NV off wipe it down with oil to gather any oxidation trash on the metal
reoil the threads and reset.

Before running I oil all threads helps to seal.
Back plate
Glow plug
Cylinder
Venturi
NV
The carb body collar if the engine is completely apart.
Crank case on the outside before slipping over the carb body.
Crank shaft and prop plate before tapping back on always use
a thrust washer steel or phenolic (I prefer phenolic less heat)