Thread:

Need advice - Excessive Black Soot on the Transom

I have a question about the “Black Soot” on your transom after a day on the lake. The history of the boat is as follows:

• 2005 26ft Cobra Razor
• 496 HO
• The boat was a repo that I picked up at the end of last summer. It only had 51 hours on the motor which as you know is really low for a boat that was 5 years old.
• I only put about 10 hours on it last summer before I put it away to begin the winter project.

I noticed that the transom was really black after a day of running the boat. I know I can expect some soot on the transom, but this was A LOT! So after doing the research I installed the following on the 496HO:

• Dana Marine Products Exhaust (Fuel pressure is set at 46)
• Whipple Stage II Tune

I was not looking to gain all kinds of power I just wanted to lean it out a bit and get the motor to breath and run and good as possible. On a positive note it definitely made a noticeable change on the power and the boat definitely has a little more punch across the board. However, this did absolutely nothing to correct the soot. After just a few runs up and down the lake I still get the soot on the transom. I know that a little is ok but this is really excessive. I have to continuously clean it off before the kids climb in the boat or it ends up all over my interior.

I have taken it so Absolute Speed and Marine and everything checks out ok on the computer. I really have no idea what to do at this point.

• Have any of you had this problem?
• The boat had low hours for a 05 so if it sat for a few years would something have gone bad (Rings, etc.) (I don’t see how rings can go bad from sitting, but I am desperate here!)
• Should I add more vents so the motor gets more air? There seems to be a lot of Cobras that do not have this problem so I do not think this will really help but once again…. I am desperate!

Any advice or ideas will be great appreciated!

Originally Posted by STV_Keith

Are you running 91 octane in it?

Yes that is what whipple recommends. I was running 87 last year before the tune.

Originally Posted by Mohave Cobra

I have a question about the “Black Soot” on your transom after a day on the lake. The history of the boat is as follows:

• 2005 26ft Cobra Razor
• 496 HO
• The boat was a repo that I picked up at the end of last summer. It only had 51 hours on the motor which as you know is really low for a boat that was 5 years old.
• I only put about 10 hours on it last summer before I put it away to begin the winter project.

I noticed that the transom was really black after a day of running the boat. I know I can expect some soot on the transom, but this was A LOT! So after doing the research I installed the following on the 496HO:

• Dana Marine Products Exhaust (Fuel pressure is set at 46)
• Whipple Stage II Tune

I was not looking to gain all kinds of power I just wanted to lean it out a bit and get the motor to breath and run and good as possible. On a positive note it definitely made a noticeable change on the power and the boat definitely has a little more punch across the board. However, this did absolutely nothing to correct the soot. After just a few runs up and down the lake I still get the soot on the transom. I know that a little is ok but this is really excessive. I have to continuously clean it off before the kids climb in the boat or it ends up all over my interior.

I have taken it so Absolute Speed and Marine and everything checks out ok on the computer. I really have no idea what to do at this point.

• Have any of you had this problem?
• The boat had low hours for a 05 so if it sat for a few years would something have gone bad (Rings, etc.) (I don’t see how rings can go bad from sitting, but I am desperate here!)
• Should I add more vents so the motor gets more air? There seems to be a lot of Cobras that do not have this problem so I do not think this will really help but once again…. I am desperate!

Any advice or ideas will be great appreciated!

Sounds like you have a typical early 496. Merc had a calibration update to lean them at idle-2000 light load. Have you done that prior to your Whipple deal? Anyway, the bottom line is usually they just run rich at low speed and cause the soot. The only proper way to correct the issue is to get into the program and adjust the parameters in which are lean. If you send us you serial number and series of numbers on the back of you ECM we can help further. Thanks