I just installed a new fuel pump on my 78. I can see fuel moving through the fuel filter next to the carb. I unplugged the fuel line bringing fuel back to the gas tank and there doesnt seem to be any fuel moving through there. Would a block in one of those fuel lines keep the engine from running? Or will there not be any gas returning to the tank unless the engine is running?

Thanks so much for the help this is going to be the baddest RV ever