Heres a few pics of the WT414.You can see the nipple in front just under the choke plate.I looked at the article i was going to post and it didnt say much so i didnt.
All it basiclly is a check valve so when you back off the throttle from WOT it doesnt 4 stroke from the plate going shut so fast and gas still coming in at full throttle.
It also helps to keep the high speed idle down also.These are the better carbs for our planes if you can get them to fit your application.
You can also see the long shafts so its easy to hook up a nose gear steering arm for a throttle arm