Disconnect the fuel line from the carburetor, open the petcock and see if fuel flows. It doesn't need to be a fire hose flow, just a steady stream. If it just drips or doesn't flow at all blow into the fuel line, toward the tank, and check again for flow. There is a small in-tank filter that threads into the inlet of the fuel petcock. It might be plugged or partially plugged with rust or dirt from the tank. This is a common problem if the builder did not clean the inside of the tank prior to filling the first time with fuel.
The kit supplied petcock allows for sufficient fuel under normal conditions. A heavily modified engine might require more fuel at a sustained wide open throttle (WOT) condition but a stock engine will run perfectly well with the amount of fuel provided by the kit petcock. There have been reports of petcocks that were not completely open when the arrows says it is and that can be confirmed by moving the lever slightly while blowing through the petcock, checking for the place where there is the least restriction. Good luck.
Tom
