The needle valve location is not going to matter. All it is is a valve. The relation of the spray bar in the carb and the center-line of the tank is what is important. Almost every person here has suggested that you switch to a smaller prop, yet if haven't seen in any of your posts that you have. This may be the single most important thing and easiest to try, Have you done it yet?

You said the engine is used. It may just not have enough compression to create good enough fuel draw to pull the fuel straight up. Especially if you tank is not right behind the engine. Did you check to see if the clunk line has come undone inside the tank? Very common.