New Carb Recommendation

What is the timing when it's in gear. It may be dropping out and you really no longer have what you think.

An XE274 is not a big camshaft. It should idle pretty easily around 800 rpm with minimal drop in gear.

Any vacuum leaks? Disconnect EVERYTHING vacuum related and plug it off. Isolate the intake tract and see if you idle changes. If idle speeds changes, you likely have a leak somewhere.