1984 Merc 75hp low top speed

[QBhoy]

Hi.
take the fin off it and trim up a little. You defo won’t see more than 40 out it I’d guess. Late 30’s would be great.

 

[thx997303]

I was wondering whether that big fin was actually causing more problems than it solved.

Should have the tach by this weekend, so I'll get a good idea what is going on then. Eventually gonna fix that hook, and the trailer.

I just noticed I seem to have some fuel leakage, so new fuel lines and we'll see how she goes.

Anything else jumping out at anyone? This boat is for fishing, and I live inland so if mid to maybe late 30s is all I can get I'll be good with it.

 

[Faztbullet]

Love that Hi speed skag loose the whale tail..move all weight to rear as if console is far forward prop has hard time lifting bow,,,

 

[thx997303]

Well, I pulled the spark plugs and found some droplets of what looks like water on my bottom cylinders spark plug.

So I'm guessing that's not helping anything. Likely dropping spark in that cylinder.

I'm going to re check compression, but given it was good before, and It hasn't overheated, I'm thinking maybe exhaust cover, or base gasket.

Any other possibilities?

 

[thx997303]

And actually, just noticed it's the bottom two cylinders.

Here's a picture of one of the wet plugs

 

[thx997303]

Seems my post may have been buried a bit. Just bumping it up. Really hoping to get this figured out soon. The water in the cylinder puts my boat dead in the driveway until I figure it out lol

 

[rat boat]

with water in the cylinders, you need to take the head off to inspect the cylinder for punctures. One of those could instantly total your motor.

 

[GA_Boater]

with water in the cylinders, you need to take the head off to inspect the cylinder for punctures. One of those could instantly total your motor.

Good luck with that. This motor does not have a cylinder head to remove.

 

[thx997303]

It doesn't? Is that not the part the spark plugs thread into?

Either way, I'm kinda guessing my exhaust baffle is the leaky part, I'm seeing evidence of even external leakage

 

[GA_Boater]

Spark plugs screw through the cylinder block cover, not into the cylinder block cover.

This cover is a water jacket for the combustion chamber end of the motor, not a cylinder head.

Use a barrel to run the motor and look for drips.

 

[thx997303]

Well, I can't do that. I've just about got the power head pulled. The base gasket is definitely leaking, so I guess off it comes.

 

[thx997303]

Well, here is what I found when I pulled the exhaust baffle etc.

I think it's been leaking right between the water jacket and exhaust upper right.

 

[jimmbo]

I thought the Bottom two spark-plugs were the ones with condensation?
The exhaust system is split into two systems, the top 2 cylinders are one system and the Bottom 2 are another, they will combine into one below in the Midsection.Examine all the gasket surfaces on the the cover and where it makes contact block and exhaust divider.
See all those bolts in the first pic, they hold down a cover/cooling jacket, that can leak and that water can be get back into the combustion chamber. Be warned, that those bolts often break when removal is attempted

 

[thx997303]

It is the bottom two spark plugs that have water in them, the top right chamber is not gasketed against cross over though. This picture of the exhaust baffle as I found it may help. Note that it is reversed. The top left in this picture goes with the top right in the previous one, and it has a mix of oil and water in it.

As an aside, I've already pulled the head cover, no evidence of exhaust in there, so it wasn't likely leaking

 

[jimmbo]

That engine does not have a removable Cylinder Head so there can't be any kid of Head Gasket Leak. The sealing surfaces on both the Block and engine cover don't look too bad. If the lower cylinders getting a Steam Cleaning, the Leak would have be below the Second Cylinder, not above or even with it. I'm going to gamble and say it is Gasket under the Water Jacket(the one with all the bolts) inside the Exhaust Chamber

 

[racerone]

You have more bolts to take out to find where it might have been leaking.----So far I do not think you have found a leak yet !

 

[thx997303]

Well, I know the power head base gasket is leaking, dripping oil everywhere.

​​​​​​The closeup is a picture of a ding In The gasket surface between the water jacket and the exhaust baffle, there is clearly lots of water in the top right of the exhaust baffle, which can Drip down into the bottom cylinders, and is shielded from the top two.

​​​​​​I've pulled the head cover, and it's very clean, no evidence of anything but water in there.

So, where to next?

As a side note, the Pistons are not steam cleaned, showing fairly normal coloration and carbon. There's no scoring evident on the Pistons, and the cross hatching is very much present.

 

[thx997303]

I removed the cooling jacket cover, can't say anything specific jumps out at me, but a section of gasket on the lower Pistons came off suspiciously easily. I'll post pics soon for some fresh eyes on it.

 

[thx997303]

This spot looks Like it may have been leaking. Any thoughts?

Seems that water jacket had some oil get into it.

As an asid, I have everything disconnected for powerhead removal, but can't get the powerhead to lift off the midsection. Any tips? Gotta get to that base gasket.

Figure since I'm this far in, I may as well replace every single gasket. Then new fuel pump, impeller, all the normal stuff. I'll also be rebuilding the carbs since if I don't I'll probably have to sooner than later lol

 

[jimmbo]

The Port Area on the lower 2 cylinders does look a lot cleaner than that of the upper 2. There appears to be some sign of a liquid at the bottom of the Exhaust transfer passage, and some missing metal there and on the corresponding location on the Jacket