I agree with "don't point it down", however, just wanted to set the record straight.

When the plane is in a dive, the fuel may or may not be at the back of the tank. A plane in a dive will probably hit its terminal velocity fairly quickly, which will cause the fuel to fall to the front of the tank. There was a video posted in one of the forums a few months back that showed this phenomenon very clearly. Go [link=http://richter-lackierung.de/aktualisierung_2006/5MBVersionflycamefuntana.wmv]here[/link] to see the demonstration video,

What keeps your engine from dying during a dive is the residual fuel in the line. When the clunk is exposed during the dive, there will be a small bubble formed in the line, which will quickly pass through the needle valve. Most dives don't last more than a few seconds, and the airplane has plenty of time to recover.

I had one plane that had a very short feed line. In a dive, the engine would die every time. I added a couple inches to the feed line, and the problem went away.

When tuning the low end, remember to make small adjustment. 1/8 turn or less, and ALWAYS reset the high speed needle after EVERY low speed needle adjustment. This is crucial to ensuring you have the proper settings. The high speed needle setting affects both high and low end.

Brad
(edited to add video link)