low_psi

Definitely don't run 91, that will cause soot. I noticed less soot on mine when I ran ethanol free. Since mine was "tuned" by Whipple to run more spark advance, it was also tuned for more fuel so I was never able to entirely get rid of the soot. Like Sydwayz said Merc, should be able to help. Heres how to do it. Get the Engine Serial Number and the PCM serial number, Call Mercury and explain your condition and tell them you heard the early 496 PCMs ran rich. They should then ask for your PCM and Engine serial number. Then they will probably tell you they can reflash it free of charge. HOWEVER, they will NOT allow you to send it to them directly. You then have to go to an authorized Mercury service facility and have them send the PCM into Mercury... If you go right to your mechanic he will most likely look up your serial number and will tell you there are no open recalls/service bulletins.... In my case I went to my mechanic first and that's exactly what happened. However, I ended up just sending mine to Whipple and had a Stage II flash put on it.