Fuel delivery issues?

I have done all I can think of. The fuel pump works, I replaced the fuel pressure regulator, had the carburetor rebuilt, replaced fuel lines as needed and had the vehicle timed. I'm getting fuel past the fuel regulator and there is fuel in the fuel bowls on the carb, but it still won't start. The carburetor is a Barry Grant 650 demon quad. For whatever reason, the carb doesn't seem to be taking in the fuel. The tank is full, and I did remove the hose from the carb inlet and put it in a gas cannot be too sure fuel is making through. I drained at least a gallon, but when I replaced the hose, nada. Please advise me what else might be the problem. Thanks