Water flow issue

[1970Thunderbird]

Hello again!

I've rebuilt my pump. I had water flowing well through the block with the lower unit off, when I attached a hose to the tube running into the block, through the lower leg. Now, with a new water pump, I have no water coming through the tattle-tale "pee" port. I figure I'm going to have to go back into the lower unit. I had the motor running for about 2-3 seconds, noticed no water, and shut it off.

What gives? Why would water flow through the block and pee port when no lower unit was attached, yet when I put on the lower unit with new pump, there's no water moving. I noticed that the ear muffs suck in a tad when the unit was running, so I presume the water pump was pulling. But the tube, from the pump to the block is clear. The water intake ports on the lower unit are clear, and I cleaned it out when I had it off the last time.

Anyone know of a good way to clean out the water passages? I'm thinking something may be blocking the water flow in the block, and there's not enough pressure from the pump to get past it, yet the hose directly to the block has no issues.

Thanks!

EDIT: Forgot to mention this is a 1978 Mercury 800.

 

[1970Thunderbird]

Re: Water flow issue

UPDATE:

If you're having the same issue, and are positive your water passages through the block are clear, try this: get a large trash can, tub, etc and submerge the lower unit and try again. I put mine in a large trash can, started it, and 5-10 seconds later, water started pouring out the pee hole. A bit after that, it came out the two square ports on the back.

Thanks for all the help and good luck to you!