Well, I drilled out the main jet to .016" as this was the size that was purportedly perfect for the Ryobi 26cc 4 stroke.
Now, top end is PERFECT. I would say jetting on top is right on.
HOWEVER... now, the engine idles very poorly.

What is strange is that the symptoms are indicative an air leak.
If I cover the carburetor air inlet until about 1/64" opening remains, the engine will idle right down to 1500 rpm or less.

I have disassembled the carburetor repeatedly, looking for any sign of an air leak. I have checked gaskets, intake manifold, everything.

The only thing that was changed was drilling out the main jet and now idle is WAY too lean to run well. The symptom are the exact opposite of what I would have expected since the carburetor runs totally from one jet.

I am about to give up on the stock WYL carburetor, but I have yet to read a single thread that suggests an EXACT replacement carburetor with two needles. Does one exist?