I have 496 Mag 375 HP with 72 hrs and I am still getting that nasty soot on the back of my boat. Would it be worth reprogramming my ECM to lean it out some. Will it hurt my motor by doing this.

What octane fuel are you running? If it is higher than 87 try running that in it. I know a guy who was having the same problem, he out 87 in it and has not had any problems since.

Are you running 87 octane? If your trying to pump a higher octane (89 or 91) in that motor you'll get more residue and your just wasting your money. Will leaning out the motor hurt it? If your running high RPM's with a lean mixture your definitly going to reduce the life of the motor over time (maybe a short time). If you get a bad load of gas onetime don't blame Mercury when something goes wrong. Richer is always better! Leave the stock motor alone and just remember to bring the Simple Green along.

Thanks guys.

I do run 87 octane to keep the soot down some. I guys I will just live with it. Better rich than lean like you said.

add a m s d box and coil ,,it will hrlp some if its not a bad problem ,,,,,6al box

I have the same thig with a new carbed motor, I pulled a couple plugs out and they looked great. i wonder how much of the soot is from inital start up and warm up time. Especially with mine having a choke.

I get the same thing from my 502 Mags. Everything I read says it's a rich map in the ECM. I can live with that as long as I am ensuring engine life.

Bruce...

Wonder what the moly on the rings are saying with un burned gas in the cylinders ??

Bobby Daniels,

I thought that the 496 motors have a seperate coil for each cylinder. Can you still add an MSD to this system??

GOOD THINKING CHECKMATE < I had to call MSD Spoke with a Msd Tech and was told they have a box just for that ?? never have seen one but he said it worked great