My O.S. .40 LA engine has been setting for a while so I broke it out the other day and got it to run except every time my plan eis in a nose attitude down it dies. Is this a carburator intake problem? What do I need to do.

With what little info provided, if your just holding the plane nose pointed down on the ground, yes it will die after a few seconds because the fuel in the tank is forward but the clunk is still at the back of the tank.

well since that wasn't enough info I guess I should add that it isn't straight up and down, just slightly about 20 degrees.

You did not say but if the airplane has been sitting with fuel in the tank and not sealed there may be junk in the tank. Fuel will evaporate. I leave fuel in my tanks but seal the supply to the pressure line with brass tubing.

Also the last flight is often a rough landing that knocked the clunk to the front. I almost always forget.
Bill

everything on the plane is new except for the engine.