The carburetor is not likely the problem. The OP has stated that the engine runs well unless it's nosed up.

Has the clunk been drilled-out so that it has a larger I.D.? How about the fuel tubing? Larger engines need larger tubing. With their higher fuel consumption, you can get drag from the narrow tubing that impedes fuel flow. Many times, you get just enough fuel flow in the level-flight codition, but when you add the chore of having to move the fuel 'uphill' (when in a climb) the fuel-line drag slows the fuel even more, and the engine leans and dies.

This was first noticed when the BGX-1 first came out...people used regular fuel line and found the same problem. In level flight, you can get just enough fuel flow, but go nose-up and the fuel flow slows enough to cause your problem.

Many times, you have to re-plumb the fuel system with the next size larger tubing. We use Sullivan tanks on all large engines, and use the next size of brass tubing, larger silicon line, drill out the clunk, and wire-tie everything in place so it won't slip off. That's cured many, many fuel-delivery problems.

Again, it's not the carb.