Mercruiser 5.0 intermittent - hard start, low/rough idle.. opinions??

[bluntinstrument]

My father's Sea Ray 215ec with Merc 5.0 2bbl i/o recently started idling low/poorly and there sounds like some kind of sputtering out of the carburetor. There is also a noise which sounds like a small metal object, like a nut, bouncing around inside the engine- irregular, not rhythmic . it stalls out a few seconds after it starts and is hard to re-start.
Carb is good(tested with good spare), ignition good (new module, full tune up)

Timing is good; compression gauge is under 15 and fluctuates rapidly

Out of nowhere the boat occasionally runs perfect with no noises at all for a short time but then reverts to the above symptoms

Am I looking at a bent / poorly seated valve? Or is there something else I should be checking? Exhaust?

 

[Bondo]

Ayuh,..... Sounds like it ain't gettin' gas,.... Check the fuel pump, the Contents of the fuel filter, 'n the fuel lines,....

 

[alldodge]

compression gauge is under 15 and fluctuates rapidly

Compression is UNDER 15 and fluctuates rapidly ??? What does this mean because compression should not bounce around and be under 15. Did you mean 150?

 

[bluntinstrument]

Compression is UNDER 15 and fluctuates rapidly ??? What does this mean because compression should not bounce around and be under 15. Did you mean 150?

whoops, it's not letting me edit it... the vacuum gauge stayed under 15 and fluttered like crazy

started the boat up tonight, and it ran perfect

 

[alldodge]

Good the hear
If a vacuum gauges flutters then the valves are leaking. The more they leak the more flutter there is

 

[vetting]

Is the oil milky at all? Seems be going around lately with water getting in the cylinders.

 

[Rick Stephens]

I had a three liter that the vac gauge readings was bouncing hard. Valves needed work. Worn valve guides will also cause this, which again means valves needing work. This makes it really hard to get a smooth low idle. At the same time, may seem fine at higher RPMs as it is much less significant with a lot or airflow. Not all that expensive a job if you can pull and reinstall the heads yourself.

Rick

 

[bluntinstrument]

thanks, i'm thinking valves also - it's been fine for the last couple of days, which means the valve is behaving for now
will probably pull the heads at some point before the valve smacks a hole in the piston