This happens with more than one engine?

If it were just the one engine you crashed, here are some things to check:

1. Crud in the needle valve. Remove the needle valve and pump some fuel in through the carburetor inlet nipple.
2. Low speed mixture set too lean. Put a length of clean fuel tubing on the carburetor inlet. Set the carb at idle. Blow in through the tubing, and turn the low speed mixture adjustment counter clockwise until you can hear air hissing from the carburetor.

If you have more than one engine with this problem, it's highly unlikely that both engines are affected by the above. The problem must then lie with the fuel system.

Make sure EVERYTHING is replaced with new, known-good parts. Pressurize the fuel tank with a basketball pump, clamp off the lines, and submerge the whole thing in a bucket of water. If you see bubbles, you have an air leak. Fix it.

Make sure the tank is LOOSELY packed in foam. If the foam is packed tight, it's no better than gluing the tank directly to the structure of the airplane.

Balance your propeller. Using the same propeller on all the engines? If it's badly out of balance, it will shake the fuel tank no matter how well you pad it.