Here's your carb picture with some markup:
In all honesty, your carb looks pretty good but one thing I have learned about these GY6 carbs is sometimes you just get a dud. This is particularly the case with the American Sportworks brands as I have had them brand spanking new with bad factory porting done and they had to be replaced.
Anyways, if your floats were sitting higher when turned upside down, I'd say you had an issue there where it was running out of fuel but yours looks fine. I am thinking possible choke issue now.
In looking at how the float works (or should), as fuel enters the carb it raises those floats up which in turn shuts off the fuel supply. Failure to shut it off can cause flooding and if it starts to do that, it should be running out the overflow tube. In even worse cases, it floods so bad that it runs into the cylinder. Fuel doesn't compress. So if it fills up the cylinder and you go to turn it over, as that piston comes up, it simply can't come up all the way and can break parts and cause damage. Worse yet, if you don't realize that is the problem, and you are checking for spark, and you turn it over and fuel comes shooting out into the spark plug that you are watching to see if it has spark...this can cause a fire, damage, injury etc. Don't ask me how I know...
Anyways, back on the subject, the other thing the float system does is make sure that there is ample fuel when the engine needs it. If the float level is set wrong in this regard, what happens (what I was considering in your case) is the fuel bowl is only holding a smaller amount of gas and when you run wide-ass-open for a bit, it uses up the supply that was there. Because the float is set wrong, it only allows so much in there and then shuts off the needle until the fuel level goes down enough in the bowl to open it again.
So the trick is to give it a happy medium. Give it too much fuel, it can flood, give it too little, and it starves for gas. Bending the tab pointed out above is what allows you to adjust when it closes off the fuel supply. Any adjustments of that tab should be done in small amounts and then tested in between to see how it worked.
Most commonly I find myself having to adjust it because the needle and seat are worn and letting more fuel get by thus it is coming out the overflow. I'll set it to where I push the tab slightly upward (from the perspective of the carb sitting in its proper mounted position, not upside down like your picture is layed out). This will cause the needle to close off the supply slightly sooner and subsequent fuel coming in will push a little harder on the needle and seat and possibly get it to seal better. That works better than 50% of the time.
Now it is still possible that the needle and seat are slightly plugged which would cause your problem If you haven't cleaned the needle and seat, tap the float pin out and raise the float whole assembly up and out of the way and then blow through the fuel inlet (seat). Wipe off the needle and reinstall. This is usually black and white meaning it is either clogged or not. If you will being a lot of these, make a habit out of blowing from the seat outward as opposed to blowing from fuel line inlet inward. Some carbs (like on a tecumseh go kart) have this little rubber thing in the seat assembly and it will shoot out like a bullet into oblivion never to be found again if you hit it with air from the fuel line inlet. Don't ask me how I know that either...it's a real drag.