NO!Is the o-ring supposed to reside on the tapered end, within the carb?
The OLDER model KLR's & KLF atv's used a courser threaded cross-top screw (fit flat or phillips screw driver), not 3mm allen bit. Those screws had an o-ring between the head of the screw & the threads. Its purpose was to seal drippage from the threads of the screw & the bore of the hole when using the tubing to confirm fuel Level like Tom's pic of yellow hose..
The float bowl in question may be from the Newer off-highway KLF / KVF atv's, which are still allowed to have the overflow stand pipes. Go figure! Bouncing around in the rock piles, the overflow pipe is more likely to occasionally drip on gods green earth.I don't know where that bowl came from, but it ain't supposed to be on your bike. The brass pipe is an overflow pipe. In the event that your fuel inlet valve should fail, that overflow will allow gas to dribble out the bottom of the carburetor instead of filling up the cylinder and causing hydro-lock. It is a wonderful idea, but the EPA made them illegal a very long time ago because, gasp, think of the children and the whales. They aren't found on modern motorcycles in the US. Certainly not on a 2004.
I would suggest either using emery cloth on the taper of the screw or replace it. And possibly use a Q-Tip & metal polish on the taper Inside the bowl, there could be 'grit' embedded into the taper. Those screws only need to 'barely snug' but people tighten the crap out of them, trying to stop a drip that can be coming from An Overflow Pipe & too high of fuel level or caused by float needle & dirt brass seat!
Then with the bowl still removed, fill it 3/4 full of gas and confirm that the taper is Not Leaking.