suction line air leak

This is my third post and from the response I have gotten, I guess I have an air leak on the suction line somewhwere. Once again, my pump struggles at kick on (30) to get going, bobbing back and forth from 25-30, A lot of cavitation at first while it struggles. Then after a long period of time it catches the water and shoots up to 50 (cut off), no problem at all once it gets going. Before this issue happened the cycle time was 2-3 minutes, its now up to 10 or more. Once it catches it you can hear a noticable difference in the sound of the pump. You then here it grab the water and take off. This can take quite some time though, like when you are manually priming the pump. My question is this. Its inch and a quarter black poly comming in. I think I am going to just scrap this line and trench in a brand new one. What kind/grade black poly do you recommend? Any other suggestions to what is causing this intial struggle to get going the pump has? Thanks...