Dang Walbro carb!
 

At the beginning of the mowing season I cleaned and adjusted the Walbro carb on my 1650. It ran really good last week until the last half hour I was on it when it started to spit, sputter, and die when I went down the small hill in my backyard. Today I mowed with it after I got my PTO adjusted and it started doing the same thing with just normal flat mowing. If I pull the choke out 1/4 of the way it will flatten out and run better. So my question is which screw do I turn out, the low idle or the high idle to get it to run better? Anybody have an extra Carter #30 they want to sell me for the 1650?

If the choke helps, then it is running lean.
Possibly there is a little bit of crud that found its way into the bowl/main jet.
If it were mine, I would remove the bowl and blow things out with air pressure.
It only takes a small piece of foreign material to partially block the jet.
Then install a small fuel filter inline to prevent future problems.

That is the reason most people don't like a Walbro, there is no high idle adjustment needle to help in those circumstances. Get you a good Kohler/Carter #30 carb that has complete adjustability.

I've been looking for a Kohler/Carter #30 carb but I haven't found one yet. Anybody have one they want to part with? When I do find one will the linkage from the Walbro work with it or will I have to get a different one?

It should work fine. Have you called any of our sponsors at the top of the page? I would imagine they have one. You might also put a wanted add in the Wanted section of the forum.