Water Pump Problems?

[BigDaddy]

I have replaced the water pump...installed an extension to the housing...Rebuilt the foot...and I still can not get the motor to pump water thru the head. Right after I did all of the maintenance to the motor while the boat was sitting tied to the dock the pump ran water thru the head and out of the hose. I am NEW to boating and realized that after we had went maybe a 1/4 mile from the dock that the pump was not pumping ant the motor was getting hot...I shut it down...got it back to the dock with thr trolling motor to ensure I did not do any further damage to the motor. I found out I needed a shaft extension...I installed it and went back to the water....ONCE AGAIN...while I was at the dock sitting still the water pump ran water thru the head and out the hose...I get upstream and NOTHING...once again I get back with the trolling motor...Pull everything apart...the housing and pump still look perfect. The key is in place on the shaft to turm the impeller.... Whats going on? Any ideas? I am seriously thinking about trolling down the river and letting the motor sink to the depths...For a FREE motor this is costing me out the rear. But I still have less than $500 in a 40 horse motor with a completely rebuilt foot, rebuilt Carb, Extension kit, and new water pump...So I dont guess I can complain...or can I?
Thanks in advance for the help. I know there are alot of people on here with ALOT MORE KNOWLEDGE than me.

[kregalmach1]

was you sure to clean the water tubes of any rubber parts from old impeller
sometimes pieces get stuck in the water tube and under power sucks it up and stops flow but sitting and idleing it dont suck it up and plug the tube completely and did you put the impeller fins in the right direction

[boats.net]

To add, varify that the water tube is sealing. Also check your poppet valve and thermostats.