Mercury 40 HP Sea Pro Rough Running with Vibration

datafan

Recruit
Joined
Apr 22, 2015
Messages
5
Recently purchased the boat/motor and know little of it's history. Here's what I do know about the motor:
1994 Mercury Sea Pro 40 hp, single carb, 2 cylinder.
Fresh fuel.
New plugs.
Spark on each cylinder.
123 PSI compression on each cylinder (according to my guage).
Carburetor thoroughly disassembled and cleaned.

I have worked on small engines and such since I was old enough to walk in the motorcycle shop with my dad, and this engine just seems to run rougher than it should to me. Although it starts right up and runs, it seems like it's missing a bit, possibly a timing or weak spark issue?

We took it out for a test and it seemed to run pretty good wide open, but has a pretty good vibration to it that you can feel through the handle at all rpm ranges. This may be a separate issue from the rough low rpm running.

Here's a video of it running today, any ideas would be appreciated! Thank You
https://youtu.be/F940eGHvvZY
 

datafan

Recruit
Joined
Apr 22, 2015
Messages
5
We took the boat out yesterday. The motor is idling rough and died a few times at low rpm, it seems to load up but unfortunately the air/fuel adjustment doesn't cure it. It's clearly missing quite a lot from idle up to about 1/4 throttle causing the motor to load up.
 
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