i have a 1973 merc 7.5hp i just put another L/U on it with a new impeller i lined up the water tube with the guide tube and pushed the L/U into place and bolted it on. the gears all work fine but can't get water pump to pee i only let it run for about 10 seconds. how long should it take to pick up water i don't want to hurt anything? Thank You for any help! Mike