Carbon/oil bubbles at water surface?

[doral270]

I have a Doral 270 with a rebuilt mercruiser 7.4L MPI. I am discharging small amounts of black material from my engine exhaust upon starting. It typically only lasts for a few seconds and I can't really determine the nature of the material. I am assuming its carbon.

I have never seen this before and I am wondering if this is something I need to be concerned about and what might be causing the problem.

 

[Reel Poor]

Re: Carbon/oil bubbles at water surface?

It's probably soot from the exhaust system. It sounds like it may be running rich.

Edit; Missed the MPI part of the post.

 

[stevieray]

Re: Carbon/oil bubbles at water surface?

Oil will give you that unmistakable rainbow that spreads out over the surface of the water - even a small drop will float up & do it. No rainbow - no oil.

 

[Bondo]

Re: Carbon/oil bubbles at water surface?

Ayuh,........... I'd Bet on a Rich running motor.......

If Merc. sets up their computers like they set up their Carbs,.......
It's Running Rich............

It's a Cost Effective way to make boats More Idiot Proof..........
For Mercruiser Anyway.......... You're the 1 Dumping the Gas in it......

 

[Reel Poor]

Re: Carbon/oil bubbles at water surface?

First you need a code reader (or someone to do it for you) to check for any codes present in the computer system.

 

[Don S]

Re: Carbon/oil bubbles at water surface?

That carbon on the water is common on carbed engines with tightly adjusted chokes, or chokes that stay closed all the time.
An MPI engine can do the same thing with a plugged flame arrestor. Or some other item on the engine causing it to run rich.
With out the proper manual you stand little chance of finding the problem. My bet would be there isn't a code set. I seldom find a fault code on EFI/MPI problems. It's always something that won't set a code.
It would also help to know what your engine serial number is. There has been several different versions of MPI used by Merc in the past. Without specific details as to which engine makes it impossible to give specific answers.

 

[doral270]

Re: Carbon/oil bubbles at water surface?

Thanks for all the replies! I had a feeling that this was the situation. I will look into it.