Poorly running Willys MB

[IvorGPW]

After having to use increasing choke to keep the engine idling and having a very leaky carburetor, I recently changed out the carburetor on my 1943 Willys MB. It now idles good but sounds like it is about to die and when revving the engine up it will either die or stumble and then accelerate. My original thought was a vacuum leak as there is an audible sucking sound but the sound turned out to be coming from the carburetor. The engine will idle all day long but runs very rough at higher rpms. The MB has a Willys Industrial engine with a brand new Carter 539s from Ron.

[GSS]

The new carbs are outstanding, but are set pretty lean. I needed about 1/2 to 1 turn of the screw to make it richer, and the slight hesitation and stumble disappeared completely.

[fiveftsix]

First thing that comes to mind here is the inlet manifold
You say it`s an industrial engine is the manifold too ??
if it is then the carb bore on an industrial manifold motor has a smaller bore than an MB or GPW one.
You might want to check that out before you mess with a new carb
Geoff Bull