1979 Mercury 115, Inline 6. No fuel on cylinder 3... Help

[Baneshecker]

Took the boat out with brand new plugs... ran for 4 hours.
Boat seemed very laggy, never really wanted to gain power.

Came home to check the plugs, All plugs had oil/gas on them EXCEPT #3. Looked brand new outta the box...

Compression was 110 to 120 on all 6 cylinders.
Spark is good.

Anyone had this problem before, cant seem to find a post with only 1 cylinder being dry.

 

[Chris1956]

It makes sense to check carb #2. I do not think that is the issue, but check to make sure it is clean. The other alternative is that you have a leak in the exhaust cover or baffle, which introduces water into your cylinder #3.

If that is the issue, the fix is to pull the powerhead and remove the exhaust cover, baffle and inner exhaust cover to replace and seal it.

 

[Baneshecker]

if water was in the cylinder, would you be able to notice it? Is there any way to test for a baffle leak on shore?

 

[Chris1956]

If you run it on muffs, with the spark plug removed, you may see water bead up on a rag held over the plug hole. Sometimes you will see rust or water droplets on the spark plug as well.

Another test is to install a dirty plug into the suspected cylinder and run the motor for a while. If the spark plug comes out cleaner, water is the likely reason....