Just bought a olin 540 1996 , I have to rev up the motor and turn up volume control very high to wash out pump.. Any ideas? I noticed I could raise top balls by stop pins but they already sit pretty close to seat ...

u need buy high quality hydraulic hose to solve this problem

?? It has new hydraulic hoses on it.. It pumps concrete like a beast, I think has something to do w balls not lifting

Check the balls to see if they're full (heavy).

Yes. Full volume full throttle when pumping water. Also, do check the balls. Sometimes they fill with water and get heavy.  if they're full, change them out. And make sure the seats are good.

yes maybe have  a hole in a ball and fille dup with concrete.

it has all new seats and balls... I noticed  the bottom balls- stop pins are all the way in and the top balls have the stop pins half inch out.. So if I screw them in the balls will be closer to seat.. But that may be a issue if a 3/4 rock gets in the mix.. A lot of rocks these days in pump mix... 

I believe you are suppose to be able to put 3 fingers between the balls and ball stop.  You do have to run at higher speed to pump water.  It is a lot thinner than concrete and takes a bit more to lift the balls to seat.