I am having Issues with my bell siphon. I have a 3/4in. standpipe and a 2in. bell. There is no issue getting it triggered, but it stops prematurely. The water level only drops 2-3 inches below the top of the standpipe. The seal is good and we have experimented with the height of the bell in comparison to the standpipe. It stops and starts fine. We had issues with starting it but now it stops early. Can anybody help?