What voltage are you running. I've found that the Sullivan likes 6 to 8 volts. I run a fully charged 6v nimh, which is about 6.7vdc and it runs better than using a 4.8vdc nicad. My first couple pumps would loose prime after a few short runs. I sent them into Sullivan and when I got them back, they worked perfect. I think the pumps need to be broke in so if you run the crap out of it for an hour or so, it might help. Just make sure its pumping fluid the whole time so it doesn't burn up.