68' Mercury 110 9.8 Overheating issues

[deftones]

Hey everyone,

I have something wrong with my 1968 110 9.8 and wondering if anyone can help me out thanks.

The problem I have is that the power head and exhaust plate start heating up relatively fast when running. I have replaced the impeller and unclogged the telltale( was clogged with dirt) and I get a steady normal stream of water out the telltale when running all the time. So that means the water is circulating throughout the whole system isnt it?This is why i dont understand how the exhaust plate and powerhead get hot when the water flows perfectly, could not find any info on this anywhere.

This outboard also "coughs" when in idle and makes a "knocking" sound that slows the flywheel when it "coughs". Runs perfectly fine in gear though.
Its also very hard to start but once started runs good despite the coughs. I did notice it looks like a little bit of exhaust comes out of the exhaust plate when it coughs. Exhaust plate gets very hot when running.

So im going to change the exhaust gaskets and baffle plate if needed. Could this be the cause of the coughing?

Im also going to rebuild the fuel pump/ and carb and hope this solves the starting problem.


Im curious if it could be something more like a lower crankcase gasket leak aswell? Could a leaking crankcase cause the "cough".I hope not but if i break bolts on the exhaust plate im going to have to remove the powerhead to repair them anyways. Unsure how to remove powerhead aswell lol. is is quite easy on this outboard?


Any help is greatly appreciated thanks!

 

[Mr. Asa]

Re: 68' Mercury 110 9.8 Overheating issues

How do the plugs look on the motor? I wonder if the engine might be running a little lean, which would cause the engine and exhaust to heat up.

Timing being off can also heat up the engine and show the same symptoms as the fuel mixture being lean, but I am not familiar enough with these motors to tell you if the timing can be changed enough to do that.

As a sidenote, I recently got a '72 Merc 110, I know I'm missing some stuff. Could you take a look at this thread and take some pictures of yours? I think they'll be close enough to each other that it will help me out
http://forums.iboats.com/mercury-ma...can-you-post-pictures-620254.html#post4321037
Thanks

 

[deftones]

Re: 68' Mercury 110 9.8 Overheating issues

Plugs are brand new and are fine. I should mention that its sparks perfectly fine and compression on both cyclinders in perfect aswell. How do you adjust the fuel? That gold screw on the carb?

Just really confused on why its heats up when water flow is perfectly normal.

And yeah i will takes some pics soon, thanks

 

[Mr. Asa]

Re: 68' Mercury 110 9.8 Overheating issues

I'm not familiar enough with these engines yet to tell you how to properly adjust the fuel flow, it will definitely be a screw on the carburetor, but which screw I can't tell you

This is a little over-simplified, and centered solely around if it is a fuel issue, also it has been a while since I have gone over the basics so I might be a little off here or there. Hopefully this will help though.

Engines at sea level require 14.7 parts air/oxygen to 1 part fuel for them to run at optimal power. If the engine is running rich at something like 11:1 Air:Fuel then the engine is going to run colder than if it's running at an optimal Air:Fuel ratio. The reason for this is that fuel takes more heat and more energy to combust than air does, so the heat goes into burning the fuel.
When you have a lean fuel mixture of 16:1 or some such then you've got an engine that is running hot. Once the fuel burns up it starts putting the excess heat into the cylinder walls and cylinder head.

IF it is an ignition issue, you can get similar symptoms because of when the fuel is ignited. If you advance the timing enough so that you ignite it early, then you're starting the combustion when there is a lean A:F ratio, if you retard the timing enough so that you ignite it late, you've effectively started combustion when there is a rich A:F ratio.


I'm not saying that's what you've got going on, but if you've got good flow with the water, I would definitely look at the carburetor and ignition.

 

[deftones]

Re: 68' Mercury 110 9.8 Overheating issues

Thanks for the info. Appreciate it. I will try and adjust the carb after i rebuild it!

Im hoping its something simple like that, i really dont want to pull the motor all apart if I dont have to. I hope after i replace exhaust gaskets it helps too. Theres obviously something wrong , there should not be exhaust comming out of there

 

[Mr. Asa]

Re: 68' Mercury 110 9.8 Overheating issues

My pleasure, hopefully it helps you out.

I am much more familiar with automotive engines than marine engines, but every carb kit I have come across has a pretty comprehensive step-by-step method of setting up the carb correctly. Just make sure you determine if there are any steps for carbs other than yours.