I am looking for others who may have run into this problem. I converted my Jabsco manual head pump to fresh water and the pump is very hard to operate. When using sea water it pumps very freely. I pulled the fill cap off to see if the tank was not venting properly to no avail.
How did you convert the head to fresh water? If you explain how, maybe something can be figured out why it's hard to pump with fresh vs. sea water.
Roc-
I put a "T" in the fresh water supply from the tank and ran it to a "Y" valve in order to select fresh or sea water for flushing. That way I can switch back to sea water when I go on a long trip. From the "Y" valve it goes straight to the head pump.
The only thought I have is the hoses that come from the water tank is 1/2 inch. The hose that usually supplies the head is 3/4 inch. Maybe the restricted diameter is making it harder to pump?? Just a guess.
Roc-
I would say you are right about the smaller hose ID being the problem. Pump designs are typicaly set up with a larger suction than discharge.
You are likely pulling a high vacuum on the suction stroke when pumping. Just pump slower on the suction stroke. the fresh water always smells better after being gone from the boat for the week.
Sanfrancisco Bay Sailin'