Black dust/soot in water after shifting into neutral

[will6181]

I recently bought a used boat with a 1989 Merc, 130HP, 3.0L inboard. I couldn't get it to idle so I adjusted the carb mixture to get the boat to idle. This worked except it kept backfiring when I tried to accellerate. I adjusted the mixture again and now I'm idling at 1500RPM which is causing hard shifting and when I put it into neutral there is a lot of black soot in the water behind the boat. I'm wondering what is the proper way to set the carb mixture to be albe to idle/accellerate properly and why an I getting all of this black soot in the water when I go into neutral?

 

[DJ]

Re: Black dust/soot in water after shifting into neutral

will,<br /><br />The balack soot is a sure sign of a very rich mixture. On the other hand, the backfiring is a sign of a lean mixture, however, you alreadty know that.<br /><br />Two things.<br /><br />I would suspect you carburetor accelerator pump is not working. Also, I think it may be time for a carb rebuild.<br /><br />The rebuild should remedy both issues.

 

[MooseHootie]

Re: Black dust/soot in water after shifting into neutral

what kind of carburetor is on your engine ? All of your symptoms you listed lead to a carb rebuild. The screws you are turning are only adjusting the idle mixture, the jets inside regulate the the fuel mixture above idle.