The high end is too lean.

Open the high end five clicks, then with the plane level run the engine up to full throttle.

Hold it there for 10 seconds or more then point the nose up.

The engine should speed up a bit and sound more powerful, but it should continue to run.

If it seems to slow down ONLY when pointed up, richen the high end needle a few more clicks.

You'll find that when everything is correct the engine will seem to run a bit faster with the nose up.

Once this is so ( assuming you have a full tank ) point the nose about 25 degrees down, and perform the same test.

The engine SHOULD slow a bit more, but should continue to run.

If all of this is working, test again with about 1/2 a tank of fuel...

Note however that on a nose down test with less than 1/2 tank of fuel, you may find that the engine will die as the clunk becomes uncovered.

This is normal, it also happens in flight, which is why sometimes people have unexpected deadsticks... not too much that can be done about this w/o resorting to bladders, etc.