I've got 2 pwk 39mm carbs I was saving for a project but no longer need them. They are both identical and in really nice shape. Looking to get $125 each plus shipping. Should be no more than $10 most places

Is that a supply line in the bowl drain? Never seen that.

I think its an extended drain. They were in a sled .

Yes they are for any dirt and water to settle down and keep away from blocking restricting the main jet.
Helps prevent blockages and corrosion to that area/jet.
On my AC550Pilot,I drilled/tapped the carb bowl drain plugs,for brass nipple and CLEAR tube for visual checks and easy draining/flush cleaning.

I remember one time at racecamp was when the Bullsbrook Knockout comps were on,my mate was having probs with his 1300BusaCuda.
It was missing,fartin',carrying on like Nukem at a Sheep auction!
I stuck my finger in his muffler pipe,damn finger came out cleaner than went in.I told him he was leaning out.
We did some visual checks,but not much till we got home.I told him to get a white icecreamm container to drain the fuel in.
There was lots of water globules in the bottom of the fuel.We found the prob.
Most of the Cuda fuel tanks are like diamond funnel shape with the E Pump right at the bottom in a circular sump.
He had a small KN style filter vent filter thingy at top of tank.I always told him to make a cover for it to stop water gettin' in thru there and into the tank.
He never did.
So the water being heavier than fuel just kept settlin' and accumalating down there right at the pump,and leaning out the fuel with water.
The combustion was so hot that it burn't a hole thru his blingy muffler.
IF he had a simple drain tube/plug setup like the sleds do,we coulda seen it thru the clear drop tube AND drained it off there and then.
It's a good idea to mod your carb drain plug and do same with barb and clear tube.

Lol!!!