Mongo's advice is spot on for a first start setup. It sounds like you are burning through the initial prime and then not drawing fuel. The problem may be somewhere between the carb and the fuel in the tank. If you put your finger over the carb opening and flip the prop, can you see fuel being drawn through the fuel line? If the throttle is open you should see fuel moving within a flip or two of the prop. This wont eliminate all fuel line problems as doing this puts a relatively strong suction on the fuel line but it at least demonstrates that fuel is actually making it to the carb. If you have an electric starter on hand, you should be able to see the engine draw fuel with the engine set up as Mongo describes. If the carb doesn't easily draw fuel from the tank your problem may be a pin hole in the fuel line or an unnoticed kink in the line. Is there a clunk on the fuel line to hold the end of the fuel line in the fuel in the tank. Basically, does the fuel have an uninterrupted path from the tank to the spray bar in the carburetor? The pitts carb shouldn't be a problem. Does it have a pressure nipple? if so, is the nipple clear? Usually there is a fuel line running from the nipple to the fuel tank vent. This uses pressure from the exhaust to pressurize the tank and act as a kind of fuel pump. Just sitting on an engine stand the engine should still run even if this is not connected but the tank does need a vent so that the carb isn't trying to draw against a vacuum in the tank. You need a path for air going into the tank to replace the fuel that is going into the carb. As I'm typing this I recall that I have more than once seen a situation where someone was setting up a new engine installation and they mixed the fuel and vent lines when installing the fuel tank. The vent line often wont be submerged in fuel. Everything looks okay but no fuel to the carb. I hope I'm not over explaining. I'm just trying to cover the possibilities without the engine in front of me.