1978 70HP Merc Hose question

[dmcomp]

Is there any 1978 70 HP Merc owners out there that can tell me where the top water hose which comes from the fuel pump goes to on "their" motor. I already have a hose that comes from the top of the cylinder block which goes straight to the tell-tale.<br /><br />Any help with this problem would be very muchly appreciated as this is the only thing left to get right before I can test the outboard.<br /><br />There are diagrams on mercruiserparts dot com, But the diagrams for the cylinder block and the fuel pump assembly contradict themselves as to where the hoses go.

 

[Chris1956]

Re: 1978 70HP Merc Hose question

Daz, The fuel hose from the fuel pump goes to the top carb. If you have dual fuel pumps (unlikely)that mount on the transfer covers, there is another hose that runs to the bottom carb as well.

 

[dmcomp]

Re: 1978 70HP Merc Hose question

Thanks for the input Chris, I will include a photo below showing the hose I have doubts about as it may be a little hard to explain.<br /><br />

<br /><br />Kind Regards,<br />Daz

 

[Kevin W]

Re: 1978 70HP Merc Hose question

The two hoses on the right hand side of the picture are fuel hoses.<br />the other two are water.<br />the top one goes to a fitting on the water jacket (i will verify where when i get home)<br />i have a 1979 70hp with the same fuel pump setup.<br />i don't realy know why they cool the fuel pump but thats what it is.

 

[dmcomp]

Re: 1978 70HP Merc Hose question

Thank you Little-Doodie, I thought it might go onto the water jacket somewhere but didn't know where exactly, Looking forward to your reply, Can't thank you enough.<br /><br />Kind Regards,<br />Daz

 

[AMD Rules]

Re: 1978 70HP Merc Hose question

On my 60hp, it had a non-cooled fuel pump, but the hose you show on yours going from the exhaust plate to your fuel pump, on mine it ran around the back of the exhaust plate to an elbow fitting on the left rear. Perhaps on yours it ends there as well, but is routed to the fuel pump along the way?<br /><br />Have a peek at the left rear corner of your exhaust plate for a tapped hole where an elbow fitting would be. It would be at the same height as the water hose you show leading to your fuel pump.<br /><br />Just guessing, but the configuration of the 3 cylinder exhaust plates look the same. I always wondered why I had a water hose that served no purpose other than to spray cold water out the upper exhaust ports. Perhaps it was a left-over legacy connection from your liquid cooled fuel pump design.<br /><br />You can see the specific connection I am talking about on the left side of this picture. Picture is looking straight down on the lower exhaust plate, powerhead removed:<br /> <br />Click to see bigger image

 

[dmcomp]

Re: 1978 70HP Merc Hose question

Here is a photo of the back of my motor, You will notice the bung under the exhaust plate, Looking through this hole I can see the flange at the top of the exhaust tube, I pushed a wire up from the top exhaust ports and saw the wire through the hole. If a water hose was connected to a fitting screwed into this hole, It would flood the leg with water around the exhaust tube and would exit via the top exhaust ports. Does this sound right?<br />

 

[AMD Rules]

Re: 1978 70HP Merc Hose question

I'm thinking the fuel coolant outlet may have originally gone directly to the telltale. Later on , when Mercury figured its better to pull the water from the top of the block (to ensure venting) they connected the telltale there instead.<br /><br />Not sure where to stick that hose, based on what you show. That plug you're pointing to may be your only option. Water will come out the upper exhaust ports.<br /><br />Hopefully Doodie will know for sure.

 

[Kevin W]

Re: 1978 70HP Merc Hose question

I checked mine.<br />Mine is connected to where the lower plug is in your picture.<br />i guess it helps cool the exhaust.

 

[dmcomp]

Re: 1978 70HP Merc Hose question

Thank's Doodie, I will get a fitting for it and will be back on the water tommorow,Can't thank you enough. <br /><br />Regards,<br />Daz