Low compression - 1986 Mercury classic 50

[JohnTRI]

I’m having low compression on cylinder #1 at 95 PSI when warm and 50 when cold. Cylinder #2 is at 125 Cylinder #3 is at 125 and Cylinder #4 is 115

Here’s a video of the engine running. I have an understanding that an engine with low compression tends to misfire and not start and if it does start it has a hard time running. I just don’t have any type of reference.

 

[jimmbo]

Welcome to iboats

It doesn't sound all that Bad, however, running on the Muffs, really does tell anyone much, as it could be running on 2 cylinders, as there is no Backpressure, not being in the water, at Docked/anchoured Depth. Running tilted like that also creates its own problems as the Fuel Level is Not as expected, because of the Angle.
Your Compression Numbers are a bit of a concern, regarding #1. It is often the cylinder to have problems if the Engine is overheated. But it might just have sticking Rings. Run a can or 2 of Mercury's Power Tune as per instructions, or a day or so before doing that, Tilt the Engine Fully up, remove the Spark Plug for #1, rotate the Flywheel until the Piston is near TDC, and spray in a several Tablespoons of the Power Tune in the Spark Plug Hole and let set. Later, before using the Power Tune according to the Label, lower the engine and crank it over to expel what is in the Cylinder, put the Plug back in turn on the Water and start it up. One thing thing though, and it is Important, after using the Power Tune, it does need to be purged from the Engine under Load, at WOT, so don't use the stuff if you can't or won't be running it on the Water at WOT

 

[JohnTRI]

I appreciate the time you took to write your suggestion. I’d like to ask another question that may be dumb. When I’m on the lake and and I WOT for about 5 minutes get to my fishing spot and troll for about 15 - 20 minutes and goto start the main motor it takes much longer to crank and get started then out of the water. Would that inability to start efficiently in the water be a sign that the compression is failing? Is there a noise I just simply do not know how to tell.

 

[jimmbo]

Lots of things can the reason it takes longer to restart when warm. Fuel Percolating out of the carbs, can create an overly rich mix getting to the Combustion Chamber, which can make starting take longer.
But first, is it cranking Slower when out on the water, versus being on the Muffs, and out of the water?

 

[cyclops222]

My 1986 and 1999 Evinrude's both start instantly hot or cold.
Remember the starter cranks the engine fast. Enough to almost fire 10 times per second. So any bad mixtures are pumped out instantly.

 

[Faztbullet]

The motor is hurt as you cant tell with it on muffs, needs to be under a load. It will still run but if it has transfer not for long. Also carbon will not build up in a single cylinder of a multi cylinder motor.

 

[Drivewayboater2]

What’s the water coming from the spark plug area at the 7 second mark in your video?

 

[JohnTRI]

Leaky water jacket and a leaky base gasket.

What’s the water coming from the spark plug area at the 7 second mark in your video?

 

[racerone]

Remove bypass cover for top cylinder.-----Inspect pistons and rings.---Easy to do and you learn lots.

 

[JohnTRI]

Today I’ve spent my time removing my power head and water jacket and these images show my base gasket and my cover gasket next weekend is when I take apart the power head to investigate. Considering this is my first time some advice on what to check and what I should clean out or maintenance would be extremely helpful.

 

[racerone]

Remove bypass cover for #1 and have look at the piston and rings.----Post some pictures of what you see.

 

[Faztbullet]

You will need to remove coil bracket an coils and need a #3 phillips bit to remove cover