1973 Merc 75 Impeller Pickup Tube

[raley]

I have a 73 Merc 75 that does not pump water well. Talked to the previous owner and he stated it never has. Replaced the impeller, cleaned out all the lines, and it still will not pump well.

I took everything apart AGAIN and without the gasket on the pickup tube, the tube appears to be far to tight into the impeller housing. Has anyone seen this or have photos of their setup?

 

[Chris1956]

Is that a 7.5HP motor?

 

[tpenfield]

The copper tube going into the pump housing needs that black rubber insert .

if the engine has over heated, there is a plastic washer up at where the upper copper tube attaches to the power head that can melt, causing restricted water flow.

that might be something to check.

 

[raley]

Is that a 7.5HP motor?

Yes it is the 7.5hp, but for what I have read, the 1973 is called a 75 instead of a 7.5

The copper tube going into the pump housing needs that black rubber insert .

if the engine has over heated, there is a plastic washer up at where the upper copper tube attaches to the power head that can melt, causing restricted water flow.

that might be something to check.

I know the rubber seal needs to be on each end of the copper tube. I was having trouble installing it and pulled the seals off to verify length and noticed what I think is too far into the housing. Wanted to see if it is correct length or if that was replaced at some point in the last 50ish years with the incorrect part.
On the washer at the bottom of the power head. I had found that last night on page 6 of this section, I will be looking at that later today.

Thank you both for the help.

 

[tpenfield]

The area where the impeller spins should be clear and unobstructed. One additional thing to check is that the metal 'cup' and 'top plate' of the pump have the positioning tabs and that they are in the proper locations, as that will be a factor on the impeller's ability to pump water.

One thing you could try is to use a drill on the drive shaft and immerse the lower unit in water . . . spin the drive shaft (water pump) with the drill to see how well the pump pushes water up the long copper tube.

There are a bunch of YT videos on replacing/fixing these water pumps. Get good at it, because you will be replacing the impellers every few years, as they wear out quickly.

 

[raley]

The area where the impeller spins should be clear and unobstructed. One additional thing to check is that the metal 'cup' and 'top plate' of the pump have the positioning tabs and that they are in the proper locations, as that will be a factor on the impeller's ability to pump water.

One thing you could try is to use a drill on the drive shaft and immerse the lower unit in water . . . spin the drive shaft (water pump) with the drill to see how well the pump pushes water up the long copper tube.

There are a bunch of YT videos on replacing/fixing these water pumps. Get good at it, because you will be replacing the impellers every few years, as they wear out quickly.

I have an impeller coming today to put it all together (whenever the mail shows up). I will give that a try.

Just to be clear, you do not think I have the incorrect pickup tube? It should be that close in the housing? (i know it is missing the rubber seal)

 

[racerone]

For many years and power ranges , Mercury used a 10X number.----The inline 6 cylinder 150 HP was designated as a 1500.----V-6 175 was a 1750 Etc, Etc.----Cut a bit off the inlet water tube to suit.

 

[tpenfield]

You picture is a little hard to see the detail, but if the copper tube is protruding into the impeller cavity, then yes the tube is not correct. It may be a matter of fitting it properly, or the tube might need a slight trim.

There is a bit of guesswork with used motors, because you never know what got done to it previously.

 

[raley]

It is fully inside the housing. So i might do a slight trim to that.

thank you for the help.

 

[tpenfield]

I see that it is into the housing, just below the impeller 'cup'. So the impeller is probably free to spin, but with this picture, you can see that the gap between where the copper tube ends and the pump housing is very small, and probably the source of your restriction.

 

[raley]

After putting in the new impeller and shaving a small bit off the pickup and re-bending it slightly, WE HAVE FLOW!

Thank you tpenfield for all of the help! now to the next problem, trying to get to the lake!