when I first start my 250, I have good return flow of fuel to gas tank. After about 15 seconds, you can see a decrease in fuel flow and it eventually peters out to nothing and then of course engine stalls. Fuel pump has been rebuilt, new fuel filter. Engine seems to run good. I have inspected vacuum hose between engine and pump. I ran a vacuum test with the hose connected to fuel pump with mityvac hand pump and no leaks. I have seen an electric fuel pump available for $38.