You are correct, the fuel pump works off the vacuum/pressure pulse from the crankcase. The vacuum/pressure pulses the fuel pump causing a diaphram in the pump to move drawing gas from the tank.
To check to see if you have proper fuel flow.........
1.) Make sure your fuel pitcock is in the on position.
2.) Make sure you have enough fuel in the tank.
I don't mean to sound like a smart ass but I have tried to diagnose a "fuel problem" with no fuel in the tank! Boy did I feel like an idiot! So make sure you check that first before preceding.
Remove the fuel line from the carb and crank the motor and see if you get fuel discharge. If you are not getting any discharge out of the carb delivery line, check to see if there is fuel discharge directly from the pump. If you get no fuel flow from the pump, you may have a faulty fuel pump.
Fuel fiflters are also an overlooked item and the fuel filter may be clogged. If you are unsure of its condition, replace it and try the aforementioned steps again.
The fuel feeding device in the gas tank is your pitcock. It has three positions.
1.) On... This is the position you should use for a full tank.
2.) Reserve... This is the position you use after you run out of gas in the on position.
3.) Off... This is the position you should use to turn the fuel off to the carb.
There is no internal feeding device within the tank other than the pickup lines for the pitcock.
As far as the throttle valve within the carb are you asking about the slide? Are we talking about a stock carb? The idle screw is located under the slide. The slide rests on the idle screw so it can't get stuck on it. Turning the screw in or out raises or lowers the slide allowing you to vary the amount of air that passes through the carb thus raising or lowering the idle.
Is this what you are asking about?