1999 Mariner 40hp top cylinder wet. please help!

tommyturbo

Cadet
Joined
Jun 3, 2013
Messages
9
Hello everyone, second time ive been looking for help since owning the boat for just over a week...

While out on the boat i notice it was getting really rough and kept stalling at low revs and as time went on it got worse.

Once out the water i pulled the plugs and notice the top cylinder (2 cylinder, single carb 40 model) was very wet.

The engine would start ok but run rough and would do a big missfire every 30 odd seconds followed by blue smoke. what was strange tho, if i added a bit of choke it would stop the big missfire but was still very rough.

So i started it with only the top plug and it was very lumpy but with the bottom plug only it was very smooth. in some ways better than with both.

So the fun begins;

replaced the plugs - same issue
swapped the coils over - same issue
did a compresson test - 134 psi on both, happy about that!

Please help as ive hit a wall now and worried its something really odd/expensive...

Thanks
 
Last edited:

Iceman66

Petty Officer 2nd Class
Joined
Jun 30, 2008
Messages
199
Re: 1999 Mariner 40hp top cylinder wet. please help!

Leaking exhaust cover plate/gasket ,crack in the block, or a leaking head gasket(if it has a head)
 

tommyturbo

Cadet
Joined
Jun 3, 2013
Messages
9
Re: 1999 Mariner 40hp top cylinder wet. please help!

Leaking exhaust cover plate/gasket ,crack in the block, or a leaking head gasket(if it has a head)

Wow that sounds bad if that's true. When I say wet it could be over fueling the top cylinder I guess.
 

tommyturbo

Cadet
Joined
Jun 3, 2013
Messages
9
Re: 1999 Mariner 40hp top cylinder wet. please help!

If it was water in the top would it run on that cylinder then?
 

Iceman66

Petty Officer 2nd Class
Joined
Jun 30, 2008
Messages
199
Re: 1999 Mariner 40hp top cylinder wet. please help!

If it was water in the top would it run on that cylinder then?

Depends on how big the leak is,will run with a small leak,but often idles rough(intermittent spark)
 

tommyturbo

Cadet
Joined
Jun 3, 2013
Messages
9

tommyturbo

Cadet
Joined
Jun 3, 2013
Messages
9
Re: 1999 Mariner 40hp top cylinder wet. please help!

Depends on how big the leak is,will run with a small leak,but often idles rough(intermittent spark)

Would I be right in thinking if the cylinder looked clean it might be water as it would of steamed it.
 

Iceman66

Petty Officer 2nd Class
Joined
Jun 30, 2008
Messages
199
Re: 1999 Mariner 40hp top cylinder wet. please help!

Yes, if you inspect both piston top through the sparkplug hole and the top cylinder piston is clean, you have a water leak.
 
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