I was hoping to get some insight on why my 1974 DT125 is dumping fuel out the carb overflow tube. Bike runs ok but as soon as I shut it off it will purge the whole gas tank. My thoughts are the carb float is sticking for some reason but i just had it all apart and cleaned. Should I be looking at an aftermarket carb or should I go back in and try to fix? Thanks for any input.

Yes, your hunch is likely correct.  Probably your float needle is not seating well.
Keep in mind that the float needle is not expected to be a "shut off" for the fuel flow.  You need to shut off your petcock every time you shut off the bike. The petcock is the shut off of the fuel.   If you have doubts about the petcock,  just pull the fuel line and see if it shuts off the fuel effectively.

Inspect the float needle and seat.  If in doubt as to its condition, replace with genuine Yamaha parts. Usually the valve and seat are sold as a unit, like at Partzilla.

www.partzilla.com/catalog/yamaha/motorcy...74/dt125a/carburetor

Is it only leaking when you stop the motor?. Maybe borderline too high fuel-float level. Gotta go in there anyway so set the float level incase its just a bit too high & spilling over the breather tube sticking up in the bowl. Plus of course the float valve--"needle & seat" as 'yamadude' says above.

If your float needle valve seat looks corroded or dirty, you can cut a high quality Q-tip in two and put one piece in your variable speed drill with a little fine polishing compound (or such)  and polish the seat at a low speed.   Then thoroughly clean with another Q-tip with carb cleaner.

Dude

Your float needle tip should look something like this, with no significant indentations.  

 

At the risk of appearing to be overly loquatious, I will add this pertinent story from last winter.
I picked up a 1982 Yamaha barn find XS650 (two cyl four stroke) not running.  Overhauled the Mikuni BS34 carbs, precisely setting the float lever heights, polishing the needle seats, and the float needles were old, but looked excellent, so I kept them in.

Started it up, and it showed exactly the symptoms you report, in one carb.
So I replaced the float needles and seats with new Yamaha parts. Result:  it fixed the problem.

The lesson seems to be (backed by other folk's experiences) that float needles can look good, but are no longer viable due to age.

I've never had much luck polishing the float needle seat...  replacing works every time.

Loquacious   I just had to look that word up  .

So you're going to make the rest of us look it up too?

LOL loquacious = talkative, wordy