Newb Fuel question

Subafly-

That's the carb vent hose. It's job is to make sure that hte carb bowl remains at atmospheric pressure so that fuel will flow. When it get's blocked off, the engine starves for fuel and runs like crap. There's a mod (T-Mod) to fix that, but that's another story 'cause it ain't your problem today.

If stuff is coming out of it then your inlet valve is definitely stuck (or the floats are gas-logged and won't float anymore) and she's floodin' like the mighty Mississippi. Best bet is to remove the carb and give it a good cleaning.

You may be able to get away with removing the float bowl and jiggling things about a bit, or you might even set thing right by tapping the bowl with a screw driver handle. But, it's a 10 year old bike. If the carb is in a state where the inlet valve is sticking, the rest of the carb probably isn't that far behind.

While you're waiting for your Clymer's to come, you might want to look at this site:

https://www.johnsmotorcycleparts.com/Keihin_CV_tuning_tips.htm

And this one:

http://www.gadgetjq.com/keihin_carb.htm

Tom

In all fairness to the shop, they have no way of controlling what will flow into the carb. A fuel filter will aid in filtering the fuel before it gets into the carb, a mechanic can not. He just can not control what is in the gasoline.
You described a "black chunk" that came out of the bowl. Since there are "supposed to be" screens on the inlets to the petcock [inside the tank], and their job is to screen impurities from the fuel, there is only one other place the "black chunk" could come from. Inside the petcock assembly, to the very rear, is a black rubber bushing / gasket. With time, it begins to deteriorate and allow small black chunks to flow into the carb bowl, causing the float to stick and flooding the bike. You can buy the "Tap Valve Gasket", as it is called, from Ronayers.com. Part # 11009-1188 for $2.54 before shipping. There is also an "O" ring gasket in the petcock assembly that should be replaced while you are in there, part # 92055-1085 and will set you back $2.02.
In the mean time, if the bike should flood out again, you can flush the little black invaders out of the bowl by backing out the drain screw on the bottom of the carb. As the gas runs out, tap on the carb bowl area to assist the contaminants out of the drain hole. Just carry something with you to back that drain screw out with. You will be going in a few minutes.
If your bike is still using the vacuum actuated fuel system, you will have to crank the bike a bit to fill the fuel bowl up enough to start the bike. The only time gas will flow from the tank to the carb is when the engine is turning over, supplying vacuum. I prefer to convert the systems to gravity feed. Rarely does gravity fail, require parts or a manual in three languages. It also limits places to look when troubleshooting a fuel delivery problem. If you think vacuum actuated systems are good, I will bet good money you never drove a car with vacuum actuated windshield wipers. You speed up, the wipers went faster. Slow down...

Anyway, based on what you have shared, I'll bet the root of the trouble is in the petcock.