Again, pardon my ignorance about combat stuff, but I see this engine has NO spray bar.  Just open venturie.

How does this work??

There is supposed to be a needle spanning the opening in side the intake.  Yes you have to run it on pressure,  crank case,  bladder or pacifier.   I used 9-7 props on mine.

Duke did not want a fat brass spray bar across the venturi to further encumber the inflow of air. So, he came up with this rather ingenious solution. Under pressure, the fuel will flow fine and and the needle will meter the flow fine. The biggest challenge was in the manufacturing process where it was important for the needle to mate properly with the opening on the inlet.

Those were a bad idea. they blew fuel 360 degrees and rarely would center in the jet. Your best option is to remove that needle and install a standard. Super Tigers worked great. I soldered a small brass tube bent 90* toward the venturi, and ran a remote OS Max needle.