I have been fighting this problem for 3 straight years. After the boat has been sitting all winter I have a real hard time getting it to pick up water from the drive intakes on a hose. I have the mercury flush muffs. It is a DWP Bravo X on 496s. Same identical situation both motors. I am watching the temp guages so they dont overheat while bringing the RPM up to 2500 while keeping an eye on the water pressure guages. The alarms are going off and I am sure I am setting low block pressure codes. This takes several minutes. Eventually once the system is full it starts pumping and everything is fine. Rest of the season everthing is fine - plenty of pressure on start up. Replaced both impellors last season. I do not have fresh water flush so this is the only way to get water into engine. What is going on with this?

nevermind me - sounds normal on the hose. You may want to add water at the seawater pump to avoild overheating the impellor.

How long does it take? When everything is empty, it seems like forever before you see water out the back.

Every year, Im just about to run up and shut mine off when they finally pump.

Im talkin 3 to 4 minutes here

You say DWP drives...Throw some shrink rap tape or plain old packing tape over the lower pickups at the bullet.
If you have the fresh water flush kit cover the other drive's pickups.
Let the water run, should come out the tails after about 2-3 mins.

have twin 598 ci looking for a type of starter motor motors crank real slow have fresh batteries and good connections any advive thanks

I would install some water hose "T" connections between the drive and the impeller, someware along the raw water coolant line, in the engine compartment. Bypass the bravo pick up all together. Run the motor with the water hose hooked up there to get the block itself completely primed. Then hook up the muffs later....much easier to suck from the muffs when the whole system is primed with water. Its a much better place to flush with coolant too... no waste from the muffs and pickups.

Another idea, still using the "T" connection at first, is to submerge the drive in a big tub of water and skip the muffs all together. Your boat, when at idle, has to pick up non pressurized water anyway.

Bellhousing mounted starters, or on the engine block ??? If you have the starters mounted on the top back of the bellhousings, then get the high torque starters that they run on the Merc 900's engine. I use them and they crank the engines just fine.

Thanks - thats a great idea

I installed flush tees on my boat. Best thing I ever did. Don't even have to close off the hose to drive. Simply attach the garden hose to the flush fitting, turn on the water. Water will flow out the drive. Then start the motor. The suction from the seawater pump will pull the water towards it and on thru the motor. No valves, no muffs, no problem.