First of all, there are Webers and there are knock-off Webers. I got a knock-off evidently. If you go the Weber route buy it from Redline Weber, not Weber Carbs Direct. Redline sells the real ones.
That being said, I bought from Weber Carbs Direct and to be honest, it ran well. However, no matter how I changed out jets and ran the best lean idle procedure, it always was a bit rich.
I never passed emissions. Last year I found someone to pass it but this year it failed again.
I replaced it with the motorcraft last weekend. It passed with flying colors! And the power and response is so much better. And, while I've only used a half a tank of gas so far, my mileage seems better.
So maybe my problems all stemmed from not having a "real" Weber. But even if the real Weber is better, I can't see it being better than the 2150.
Price is comparable ( I think the MC is a bit more) and the MC is much easier to tune and work on.
Others can speak up, but my advice is to buy the Motorcraft.
1989 YJ - 4.0L
2001 WJ 4.0L