It's on a carb for an older chipper that's not running for another reason, I think. I thought it was for draining the bowl when I was putting it away last year, but apparently not, and I'm not sure what it does. It has a spring on the outside and has a needle-like appearance when removed. The air comes in from the side. Thanks.
This looks like a typical Marvel - Schebler Carburetor. If so, that's the main jet adjustment. The idle adjustment is that screw on the top body coming in from the right side. The float level is adjusted by bending a tab on the float. A Google search will get you lots of diagrams. If I remember correctly, adjust it this way. Try starting it with the main jet about 2 turns open. Once it's warmed up, adjust the low idle, then adjust the high idle to maximum rpm, then richen it by backing out the main jet screw half a turn. Leaving it leaned out to maximum RPM will get you burned valves. I put many barrels of gasoline through one of those on the old Cockshutt 30, but that ended 40 years ago and my memory isn't the greatest anymore.
Updraft carb on a Briggs? (Shudders......) Needle screws with springs are generally fuel adjustments.your bowl drain is actually the main mixture adjustment screw. Nothing wrong with draining it that way just put it back exactly where it was or be prepared to re-tune.
Some carbs of that style on a Briggs had a long brass tube up above the main (high speed) jet screw. It's real easy to wreck it if you separate the top and bottom halves of the carb, which is necessary to set the float level or do a thorough clean-out. So take out the main jet and the hex-headed bushing it screws into. Turn out the bushing and the main jet screw as one piece. Look in the hole and see if what looks like a brass slot-headed screw with a hole in the center is up there. If there is, screw it out. You may have to grind the side of a screwdriver to fit, as it may be too tight for an extra thin blade. When you get it out it will look like a long brass tube with a hole drilled crossways through it about half ways up. I knew one old boy who could wiggle the top and bottom apart without wrecking the tube, but a lot of guys ended up buying new tubes. They'll kink at that hole in the middle and then they are toast.
