It's brand new. And doesn't work.
If you think the choke is the problem--most likely meaning it's not opening when the engine is fully warmed up and thus shouldn't stumble--block the choke to full-open somehow (ziptie in the choke linkage, remove it, etc) and see how it performs when nice and hot. If it's still stumbling, you have other problems, likely accel pump.
If you think the choke is the problem--most likely meaning it's not opening when the engine is fully warmed up and thus shouldn't stumble--block the choke to full-open somehow (ziptie in the choke linkage, remove it, etc) and see how it performs when nice and hot. If it's still stumbling, you have other problems, likely accel pump.