Hey, Adrian. A couple brief comments and questions. From your pictures, it looks like you've hooked up a fuel tube to that extra tube stub that comes with the WT456, and I see it's full of fuel, too. What are you doing with that? On my Saito 150/wt456 conversion I have this blocked off with a cap and it works fine. I think that's a tank return line for carbs with a primer bulb, which you don't have (going from memory here folks...). As long as your choke is working you should get plenty of fuel to start the engine.

Eventually, those black reed valves give up. If you're not having issues now, you will. Get the teflon impregnated glass one on order now, via a rebuild kit for that carb. The blue mylar version works too.

Regarding your suggestion to reorient to horizontal the metering hole; On my engine, the metering hole is DOWN, like your's. And it works fine. Just to make sure we're talking about the same thing, the metering hole (to ambient) is the little hole in the metal cover (4 screws) on the side of the carb opposite the pump cap (1 screw). It's purpose is to provide a reference pressure to the diaphragm below that regulates how much fuel is available to the needle valves upon vacuum demand inside the venturi. If any ram effects from relative wind inside a cowled installation are present, the pressure on the reference port can rise, leading to a rich condition.

Outside the cowl, out in the open, and protected behind the cylinder head, it's doubtful you're having metering problems based on this hole pointing down. Now, I don't know what you mean when you say your metering hole is "UP". Your pic shows it down I think. Is that an old picture you posted earlier? Even your sketch shows the metering hole down. But in the sketch, you refer to your "new idea" of the "pulse pump", too. This adds to confusion over what you are really talking about reorienting. Pulse pump? or metering hole, as in the text?

Regardless, don't go to too much work to reorient the entire carb as my opinion it's doubtfull the position is affecting your engine. Is there either sealer, or a gasket on both side of the carb spacer? If it won't run at idle, it should also be almost impossible to start by hand. Is it? When you choke it before applying spark, is the carb a lttle wet? it should be, especially with the carb pointed down. Is one of your idle ports blocked? If all simple fixes fail, blow it out with an airhose to make sure (carb disassembled). This is so dumb as to not be worth mentioning, but your pic shows the external idle set screw engaged with the throttle plate. Back that screw off. It may be limiting your idle low speed.