black soot / backfiring

[traveling man]

I have a 1994 3.0 liter merc 4 cyl. This was my 3rd time out this year with the boat. First time out trolled for 5 hours and headed back to port and it did not want to go fast. It back fired when i gave it gas. After slowing down and speeding up a few times it ran fine. Went home and changed the plugs. 2nd time out same thing but i noticed some black soot on the back of my boat. today after trolling i put the boat in neutral and gave it some gas, a lot of black soot came out of the exhaust and floated on top of the water. Put it in gear and it did its backfiring thing for a few minutes then ran fine then after a mile or 2 it started backfiring again. Then it ran good again. Any suggestions where i should start on fixing it.

 

[Haut Medoc]

Re: black soot / backfiring

Change your water separating fuel filtr.....
When was the last time a full tune up was done?......​

 

[traveling man]

Re: black soot / backfiring

about 5 years ago. should i start there?

 

[Haut Medoc]

Re: black soot / backfiring

Yes, you are overdue....
& change that filter.....​

 

[traveling man]

Re: black soot / backfiring

i pulled the spark plugs again and they were wet and dark. The cap looks warn, the rotor is black and looks burned down by the block. What else should i change for a full tune up? I can not find a fuel filter.

 

[Haut Medoc]

Re: black soot / backfiring

If you have a 3.0 you might not have a water separating fuel filter...
But you should install one....
Check the screen at the inlet to the carb for debris.....
A full tune up would be cap, rotor wires & plugs at the very least & retimed....
That procedure would depend on what ignition system you have......​

 

[Bondo]

Re: black soot / backfiring

What else should i change for a full tune up?

It sounds to Me, that you'd better include a Carb Kit too.........

It's running Too Rich in the low-speed circuit,+ Too Lean on the high-speed side.......