[G.M.]

When you shut the engine down the manifold and carb are very hot. Gas evaporates from the heat and even more evaporates over two weeks of sitting. With a bad flex line and poor check valves the fuel in the pump and fuel lines drains back to the tank and it is almost impossible to start by cranking without starter fluid or gas down the carb. The gas in the carb can not drain back to the pump or tank. With a good flex hose,tight connections and a working check valve, fuel is trapped in the pump and lines and in 4 or 5 revolutions of the engine gas is pumped to the carb and it starts. The fuel in the pump, flex line and supply line are like a straw stuck in a glass of coke, pull the hose out of the soda and the soda drains out of the straw. Hold your finger over the straw and the soda stays in the straw when lift it out of the glass of soda. The check valve is the same as your finger over the end of the straw, in this case the check valve is your finger. G.M.