1984 Merc 75hp low top speed

[thx997303]

The missing metal happened on disassembly. It was me. That area is not a sealing surface, but I'll be fixing that before reassembly.

Here are the things I'm noticing, marked in the pictures.

Note that the right side of the sideways picture seems to go nowhere.

 

[jimmbo]

Clean the Surfaces and then check them for warping, gouging


are you saying the circled area is not a sealing surface?

 

[thx997303]

Yes, that area does not seal. Here's a picture with the shape of the gasket for that area.

At this point, I need to find the leak just To verify it hasn't got a pinhole somewhere. Of course that looks pretty unlikely, very little corrosion on this powerhead.

 

[jimmbo]

That Cover that you just removed is Prone to Warping, especially if the engine ever got a bit Warm. Check it for warping with a Straight Edge. The reason there is no gasket there is for drainage of any water/fuel/oil that may accumulate there(water is on of the Products of Combustion), otherwise a build up of any of the above could Hydro-lock the bottom Cylinder as the Exhaust path is upward for the bottom two cylinders

 

[thx997303]

That makes sense. I'll see what kind of straight edge I can get a hold of tomorrow. Any suggestions on type it straight edge for this purpose? I've only got your typical squares and such used in construction. May not work in this application.

 

[flyingscott]

A Google search suggests is is actually a 13 1/4 x 17 pitch prop, and it seems by some calculations, it's probably going exactly the top speed it should.

Would it make sense to go with a steeper pitch and test rpm? I really feel like this 75 hp outboard should be able to push this boat faster. I've seen similar boats with 50 hp outboards exceed 40 mph.

Where are these boats?

 

[thx997303]

It's possible I've misremembered numbers from other people..... Likely even.

But back to the current situation, which is the water where it's not supposed to be....

 

[thx997303]

Ordered a new water jacket cover and a full gasket set yesterday.

​​​Still need some help figuring out removing this powerhead.

 

[racerone]

Step #1 is to remove the piece below the lower cowl.---Horseshoe shaped item.

 

[thx997303]

Maybe I wasn't clear, but everything is removed, cowlings, shift and throttle cables, nuts holding the powerhead to the exhaust extension, etc. With all of that removed, I cannot get the powerhead to budge.

 

[thx997303]

Managed to pull the powerhead. Base gasket definitely leaking. But I'm having issues understanding the water path. And for some reason I can't get photos uploaded.

Could The leaky base gasket cause the problem?

 

[thx997303]

Waiting on parts but man.....somebody has to have some insight on whether the base gasket could cause this issue...

 

[jimmbo]

If the Base Gasket is leaking and Water is getting into the Exhaust, normally you would think it would just flow down and out. However, with Exhaust Tuning, maybe. I don't know if the Pressure Pulses can push Water back that far. Water leaking near the Exhaust Ports certainly.

BTW, the Photo Upload is working again, for now anyway

 

[thx997303]

Thanks for letting me know about the photo upload! Was beginning to think I exceeded some limit I wasn't aware of.

Well, the base gasket is the only gasket I can say for sure is leaking. It's really got me frustrated. I like to confirm the problem before attempting a fix, but this powerhead is making that difficult

 

[jimmbo]

I see a torn Gasket. Was that part of the gasket missing? Had it slid in or out? Where was the leak? Check the Base for warpage too.

 

[thx997303]

The piece between the two Exhaust ports was covered in Black and lifted from the surface, I pulled it off before taking the picture for some reason, but that was definitely leaking.

That gasket was also leaking oil externally before I tore the powerhead down.

I've been looking for the source of water getting into the to bottom cylinders. When I tore it down, I also found water oil mix high in the powerhead.

Here are some pictures from earlier.

 

[thx997303]

Well, I've pretty well re-gasketed the entire outboard.

Got everything together, and a ground wire started smoking when I used the trim. Found the battery dead, causing a high and draw. New battery and amp draw it normal with no smoking.

Went to turn her over, and sounded like it wasn't getting fuel. Turns out the old house collapsed internally.

New fuel hoses later, and I confirm I'm getting fuel because now the fuel filter housing decided to leak.

Replace the o ring there, and she fired up after some cranking, likely to fill the fuel bowls.

Good strong stream from the tell tale, which is great since I replaced the impeller and resealed The foot.

Hooked up an inductive tach and loaded up to take it to a lake and do some testing, get about halfway there and realize the registration is expired.

Well, soon I guess


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