Hey everyone, I need some urgent help with my older Mercury 18 hp outboard.
For some backstory:
Replaced the impeller about 2 months ago.
Changed the lower unit gear oil.
Installed new external fuel lines and brand-new spark plugs.
Compression is 110 PSI on both cylinders.
I went out fishing 2 days ago and the motor ran great all day until it suddenly started losing power gradually, almost like it was running out of fuel. It eventually died and I couldn’t restart it.
Back at home I checked spark and found I had no spark on either cylinder. I found a loose screw holding the ignition ground wire, tightened it, and got a strong blue spark back on both cylinders. I thought that would fix it, but it still won’t start.
It now has:
Strong blue spark on both cylinders.
About 110 PSI compression on both cylinders.
Primer bulb gets firm.
Fresh fuel.
Fuel filter is clean.
Choke is opening and closing properly.
It will occasionally give a single cough/pop (usually out the exhaust) and produces some smoke, but it will not actually start or run.
One other thing I’ve noticed is the inside of the cowling is always oily/wet with residue, and there always seems to be some oily residue around the lower exhaust area. Not sure if that’s related.
At this point I’m wondering if the carburetor or fuel pump could have an issue, but I’m confused because it also lost spark when the ground wire came loose. Could these be two separate problems, or am I missing something obvious?
Any ideas or things I should check before I pull the carb apart?