My HP500EFI's still run and sound fine, but the transom on the port side is suddenly covered with black soot. I have Silent Thunder.

Could a stuck injector cause this ?

Any other ideas?

Thanks!

How old is the gas?
Was it running to cold, stuck open thermostat?
Did you put in a higher oct. gas?

Gas is fresh, from a high volume gas station.

Good ol' 87 octane.

Was not running cold, but I did recently pick-up sand, causing the water temp to rise to 200 before I shut it down. Replaced the impeller, and temp and oil pressure are normal. Oil looks fine, and level is unchanged.

Scan it to see if all the sensors are working and ok, it may think it's cold and has it running rich.

You could swap ECM's and see if the problem moves, But I would bet it's a bad sensor or something like that.

Thanks.

Sounds like the choke isn't opening fully when the engine gets to temperature.

500 EFI, no choke