why?

[cosworth34677]

ok don't know how to fix this ? ok when i test my hydraulics in a bowl of fluid
the rams and pump work crazy good! fast no lag and problem. buy the moment i put the little fitting back into the tank it slows down and acts sluggish and like it's got a block of some kind? why is this? i don't want to hurt anything if there s is a ! any ideas why? the tank is a fuel tank for a air plane and i'm useing the old magom hrc rams and v1 pumps and v3 valves,