Since you mention a minor crash, it's possible that the klunk in your tank is stuck at the front, and therefore isn't drawing fuel correctly. That's my first guess.

Other possibilities include holes in the fuel line, or other air leaks in the tank/fuel system.

The needle valve you found is the high-speed needle.

I'm not sure about the carb on the Megatech .46, it might have a second needle or low speed, or it might be an "air bleed" carb. I know the Megatech .15 uses an airbleed. Does your carb have a really small hole in the front of the carb, and a small screw that partly covers it? If so, that's an air bleed carb. That screw is your low speed mixture setting. Check to make sure that hole doesn't have any thing in there blocking it.

If the carb doesn't have an air bleed on the front of it, then it's likely a two-needle design, and the low speed needle is usually that little screw in the center of the thottle arm.

The important thing about low speed mixture, weither air bleed or two-needle, is that it doesn't affect the full thottle running (much). So, if you are having the problem with the engine dieing when you tilt up the nose, it's not the low speed setting.

As a general thing after a crash, you should check carefully for any junk getting in the carb.