Intake manifold gasket leaking?

[BarryTurano]

Have been dealing with this problem for what seems an eternity. Boat will run fine while cold after running for an hour or more it will bog down when accelerating. It will eventually keep losing rpm's. There is also a smell of raw fuel. It acts like the motor is loading up with fuel. The carb has been rebuilt twice. Same problem still exists. Mechanic found that the bowl was empty after standing overnight. Filled the bowl with the fuel pump pinched off the fuel line so it would not flow back to the tank (it wouldn't do it any way, anti siphon valves). The next morning bowl was empty again. Took off the carb intake manifold was full again. Brought the card back to the re-builder. He did a bench check and found nothing. Needle and seat were OK. The well plugs were sealed with epoxy and not leaking. Found rust on the stbd side of the bottom of the carb. Image attached. Re-builder is making up another carb. He has suggested that it may be a intake manifold leak. I know that it is not a head gasket I see no water in the oil, and I think if it were a bad head gasket it would run like crap.
Forgot to mention it is a Volvo Penta 5.0 carbed with HEI ignition with mechanical advance. Just changed it from a vacuum advance.
Any ideas? Thanks in advance.

 

[Lou C]

There is a water passage in the front of the intake manifold that gets water from the front of each cyl head and it is possible to get a water leak there. But you should see rust in the manifold under the carb on the side where you saw the corrosion. If there is a leak there fix it promptly because it can put water in a cylinder. Eventually the oil will start to get milky as well. If you suspect an intake msnifold leak remove the fro t 2 spark plugs on each side and check for rust on the electrodes of the plugs (water in a cyl will also turn the center insulator orange). If you disable the ignition, remove all the plugs and crank the engine over for sure you will know if there is water in a cyl because it will shoot out of the plug holes.

 

[BarryTurano]

Plugs were clean a few weeks back when I changed them. Just seemed fuel fouled. No rust or water in the cylinders. Carb guy told me if the leak is by the air intake it would not idle. If the leak is near the fuel port it will run rich. The strange thing it is only on the STBD side. The port side is clean.. Each time the carb has been removed I find the same thing. Will be changing the gasket tomorrow, hopefully it solves the problem.

 

[bruceb58]

How can the leaking of a carb float bowl have anything to do with an intake manifold or intake manifold gasket?

Sounds like a bad carb body. What is the history of this carb?

Also sounds like the carb guy is trying to throw you off track away from something he doesn't know how to fix by mentioning the intake manifold as a reason the float bowl is draining.

 

[BarryTurano]

I don't know just grasping at straws. This carb was out in this past October. It was a replacement for the one installed the previous May. Both have acted the same way. Both have shown the exact same corrosion. Seems odd that 2 different carbs would act the same way. That is why I am replacing the gasket. It is the only thing that has not been changed in the entire system. It used to be injected, now carbed, distributor was changed to HEI that was vacuum advance to mechanical advance. 5 to 7 psi fuel pump was changed from the 15 psi lp pump when it was injected. All fuel lines have been replaced. Tanks were cleaned and flushed when I bought the boat. Have run about 1200 gallons of non ethanol fuel since I got the boat. Thinking of re-naming her "box of chocolates" just ask Forest Gump.

 

[BarryTurano]

No Title

I think the problem has been solved. Found a crack in the intake manifold gasket (image attached). Changed that. Carb was rebuilt again, this time the jets were changed to the size for a 5.0 not a 5.7. Hoping that was the cause of the over fueling. Put in the Davis Unified Ignition with mechanical advance. Humpty Dumpty is back together and resting. Tomorrow we will re-time the motor and test it out. I feel positive about this now. Fingers crossed.