Mercruiser inboard starving for air?

[dm2528]

Hello, I have a 1988 31 Pacemaker sportfisherman with twin Mercruiser 5.7 bluewaters. I have been having problems with low power (RPMs) in the port engine at first I suspected it was starving for fuel which I have ruled out by replacing all filters (yes the one in the carb also) and testing fuel pressure which is 9lbs at wide open throttle. It was during this test that I discovered that when the engine hatch is open the engine picks up 500 or more RPMs as soon as you close it it drops off again. I have checked the side air vents for blockage. I am not sure what to check next

 

[180shabah]

Re: Mercruiser inboard starving for air?

If the vents aren't blocked then they are inadequate. You need either more or larger vents.

I doubt it left the factory witht this problem. Most likely there were additional passive venting areas (around seats, through compartments, etc) that are now either blocked by gear, or intentionally sealed by a previous owner. You could try to re-open these and then see if you get your power back.

OR

shop for bilge vents.

 

[45Auto]

Re: Mercruiser inboard starving for air?

Is there a bulkhead between the port and starboard engines? If there is not, it's hard to understand how this "air starvation" problem is only affecting the port engine.

 

[180shabah]

Re: Mercruiser inboard starving for air?

nice catch - i missed the dual engine/single problem part.

 

[oops!]

Re: Mercruiser inboard starving for air?

i am not a mechanic......so for what its worth.

the problem as stated is not factory....i would also look for an intake manifold leak on that side.

one of the tricks i had discussed with local mechs is to add a 4 inch air hose from an out side vent and lay it right beside the air filter. this was only to get cool air form outside into the carb. but in your case it might be the band aid you want.

 

[dm2528]

Re: Mercruiser inboard starving for air?

There is no bulkhead between the engines I have noticed a small exhaust leak between the riser and the muffler. Is it possible that it is bad air and not a lack of it?

 

[QC]

Re: Mercruiser inboard starving for air?

Is it possible that it is bad air and not a lack of it?

Yes, you could have your own little custom EGR system, but I doubt it. Is there anything on the hatch itself that might obstruct air to the port engine when down? Closer to the Spark Arrestor? You could try running without the spark arrestor fo a minute and see if that fixes it. Could eliminate the exhaust recirc concern too.

Edit: Maybe some insulation that hangs down only when being "sucked on" . . .

 

[dm2528]

Re: Mercruiser inboard starving for air?

Engine covers are flat with no insulation
here are a couple links to boats that are the same

http://www.yachtworld.com/core/list...087/Solomons/MD/United-States&boat_id=1622087

http://www.yachtworld.com/core/list...8/Ocean-City/NJ/United-States&boat_id=1944028

 

[QC]

Re: Mercruiser inboard starving for air?

Well on the first one there is a kayak blocking the starboard vent, but your problem is port, hmmmmm . . . .

Beats me, and the single engine issue is odd for sure. Just get a sawzall and be done with it