new boat to me 03 formula 312 w 496 ho.s motors turn 5000 all stock 160 hrs motors seem to run excellent . i removed the silent thunder platform an installed straight tips . problem is back of boat is all black from exhaust i think their was a recall at 1 time reguarding this anyone have any ideas or suggestions . i dont think their is any problems w motors just rich running

If desired, you could add the CMI exhaust that supposedly adds 50-60hp which would help "lean" the motor out too. (sounds like a win/win)

I think this is fairly normal. Everyone ive seen leaves black on the back of the transom. I guess it just depends on how much you are talking about.

"supposedly" being the key word

Cured my black transom problem...

For some reason, I usually only notice exhaust soot when the water is cold.

I ran into this issue when I purchased my '03 Sonic. The transom would be completely black after just an hour of use. It was sticky and tough to remove. There was a recall on the ECU's in 2003 that was never performed on my boat. It has something to do with incorrect voltages to the fuel injectors. I worked with Mark at Precision Marine(pmefi.com) to get the updated program. Now, I only get a light film that easily washes off.

It helped with mine too. I was commenting on the 50-60hp increase claim.

Run your ECU S/Ns through your closest Mercury dealer. You will can either get a reprogram or new ECUs, depending on the models.