Ford 4100 Secondaries

I have a 1964 Ford 4100, 1.12 bore, on my 1965 Mustang 289 with Hi-Po cam and Ford aluminum hi-rise manifold. I can't get the secondaries to open once the engine is started. They open fine when engine is stopped. I did notice that the ball check was missing but that should only make them open faster, if my thinking is right. My question is if I need the ball check where can I buy one and if not what is causing them not to open when engine is running?