Smoke and rough idle 4.3 (UPDATE)

Discussion in 'Sport Boats' started by dlows185, Sep 23, 2021.

  1. dlows185

    dlows185 New Member

    20
    Nov 3, 2017
    2004 185 Sport 4.3 Mercury
    4.3
    Had the boat on the river yesterday. 2004 185 Sport 4.3 153 original hrs. I went to put the boat in neutral after a 30 mile run at 3k RPM, and noticed the idle to be rough and almost wanting to die. I never let it stall out before bumping up the throttle. I also noticed white smoke and a heavy fuel smell coming from the back. The boat has always ran great, an i have had very little issues over the 5 years i have owned it. 2 weeks ago ran great no issues.

    I decided to keep the boat running and take it back down river to where launched it. After docking it, it wouldn't start back up. I had to give it some throttle and it eventually it turned over. I'm thinking it was flooded. The boat is running great at speed.
    After i got the boat out of the water, i noticed black stains on the horizontal area of the transom.

    Is my boat running rich? What could have happened between now and 2 weeks ago when the boat was running fine?
    I guess I'm asking where to look first in CSR expert opinions.
    Thanks!
    Derek
     
  2. Little Ducky

    Little Ducky Well-Known Member

    Jun 5, 2017
    Dickson, TN / Chattanooga, TN
    1998 290 Sundancer
    Twin EFI 5.0L w/Alphas
    Kohler 4kW
    White smoke could be water somewhere it's not supposed to be.

    How's the oil? Milky or clean?
     
  3. BillK2632

    BillK2632 Well-Known Member SILVER Sponsor

    Jun 25, 2009
    Lake Norman, NC
    1999 185 Bowrider,
    Mercruiser 4.3, Alpha I
    A rich running engine=black smoke
    Oil burning=blue smoke
    Water/antifreeze burning=white smoke

    And it is still running fine at speed, just won't idle? Is this the original carburetor? Do you run ethanol fuel?

    Like mentioned above, check the oil for water - if the oil looks like coffee, stop, it's not a carburetor problem.

    Assuming it is smoking black fuel rich smoke, I would:
    Change the fuel filter (pour the contents into a jar and check for water or debris).
    Check / clean the carburetor input filter.
    Get some carburetor cleaner and clean it real good - spray the cleaner all down the throat and into the tube in the middle of the carburetor - this will get the cleaner into the bowl and float.
    If you find debris in your filters check the fuel line - if it is original, it is likely deteriating from inside and it is time to replace.

    If none of this helps, you probably have an issue with the float/needle/seat. This basically meters fuel into the carburetor bowl - a lot like a toilet bowl. The float can deteriate over time and with ethanol fuel and start not working properly. It could be time for a carburetor rebuild.
     
    Last edited: Sep 23, 2021
    WaveDancer01 and Little Ducky like this.
  4. Thornton69

    Thornton69 Active Member

    804
    Sep 15, 2014
    Northern BC
    1981 245 SDC
    2021 Solar 420
    '97 5.7 Bravo 2
    '20 Merc 25 EFI Jet
    Is the choke plate fully open?
     
  5. BillK2632

    BillK2632 Well-Known Member SILVER Sponsor

    Jun 25, 2009
    Lake Norman, NC
    1999 185 Bowrider,
    Mercruiser 4.3, Alpha I
    Good point, I would put this on the short/cheap/easy things to check. That boat most likely has a 2bbl Mercarb and an electric choke, the power leads to the choke have been known to come loose, get corroded and generally just not work right.
     
  6. dlows185

    dlows185 New Member

    20
    Nov 3, 2017
    2004 185 Sport 4.3 Mercury
    4.3
    It runs great at speed. I run 91 octane from Chevron pump and add StarTron treatment. Original carb on the boat, yes.
    I dont remember the smoke being dark. Ill check the choke my next time out and then go with cleaning the carb next. I change the water separator each year when i do oil and gear fluid. Never seen any water when i pour it out. Thanks for the responses everyone!
     
  7. electricaldoctor

    electricaldoctor Well-Known Member TECHNICAL Contributor PLATINUM Sponsor

    May 14, 2008
    Thousand Islands, Rockport, Ontario.
    1988 390 EC
    454 Mercruiser Gassers
    White smoke could mean a leaking head gasget. Do not run engine any more until you rule this out.
     
  8. Arminius

    Arminius Active Member

    629
    Oct 30, 2019
    Seattle
    Bowrider 200 Select, 2003
    5.0L MPI, 260 hp w/Alpha 1 Drive
    Run the blower for 5 minutes before trying to start it up. Gas fumes plus air in the right combination explode with a force often compared to dynamite. Given your unknown malfunction, you should take care and consider whether a fire on your boat would spread to others.
     
  9. Thornton69

    Thornton69 Active Member

    804
    Sep 15, 2014
    Northern BC
    1981 245 SDC
    2021 Solar 420
    '97 5.7 Bravo 2
    '20 Merc 25 EFI Jet
    Had a choke unplug and get lazy on us once. Started cold and ran fine above idle. It did sputter and struggle to keep running once returning there though after warmed up. Another common problem that the op mentioned was the accumulation of soot behind the transom. Remember smelling and seeing exhaust as well but don't recall it being white. Plugged it back in and the problem was gone.
     
  10. Arminius

    Arminius Active Member

    629
    Oct 30, 2019
    Seattle
    Bowrider 200 Select, 2003
    5.0L MPI, 260 hp w/Alpha 1 Drive
    Actually look at choke plate. Not personally familiar with that carb but>>. With cold engine, put on your safety glasses and remove flame arrestor. Look down carb throat, choke plate should close it off. Start engine, plate should gradually open because a heating element is warming a piece of spiraled bimetal on side of carb causing shaft to turn. don't think you have to "unload" those but you might shut off engine and then blip throttle and see if plate has opened. heating element is modern/boating substitute for heated coolant which took a while, causing pollution. A closed plate would cause a warm engine to run rich and produce black smoke.
     
  11. dlows185

    dlows185 New Member

    20
    Nov 3, 2017
    2004 185 Sport 4.3 Mercury
    4.3
    Thanks for all the responses. Ill be able to get to the boat tomorrow and check the choke out first and then go from there.
     
  12. GypsmJim

    GypsmJim Active Member

    588
    Aug 8, 2018
    Western New York
    '19 SPX 190 OB, 150 & 5 Mercs
    '17 Whaler 150 Montauk
    '15 Yamaha FXHO
    '60 Mulray Dinghy
    '52 Lyman 15'
    Mercury 150 4-stroke
    68 Outboards representing 11 manufacturers
    I've had similar problems every few years.

    White smoke could also be steam, coming from a hot exhaust, the right air dew point, etc, etc.

    Check the oil for water intrusion. If there is some, stop right there.

    If the oil is OK, run the engine at fast idle and spray a can of gumout into the carb. It will want to stall. When you can spray full blast and the engine won't die and all you see it white smoke, the carb is clean. Works for me every time.
     
  13. dlows185

    dlows185 New Member

    20
    Nov 3, 2017
    2004 185 Sport 4.3 Mercury
    4.3
    UPDATE:
    Whet to boat storage today to look at the carb amd choke. Pumped the throttle once to close the choke and turned the ignition on to see if it would open over time. Never moved after about 3 minutes. Checked voltage to the purple lead that hooks to the choke and a good ground and got 0v.
    This should be reading some voltage with just the ignition on, correct? Or does the engine need to be running?
     
  14. techmitch

    techmitch Well-Known Member PLATINUM Sponsor

    May 1, 2008
    Chesapeake Bay, Middle River/Frog Mortar Creek MD.
    1999 270 DA
    Twin 4.3s W/Alpa I Gen II's
    Some if not all get their power from the alternator and must be running.
     
  15. GypsmJim

    GypsmJim Active Member

    588
    Aug 8, 2018
    Western New York
    '19 SPX 190 OB, 150 & 5 Mercs
    '17 Whaler 150 Montauk
    '15 Yamaha FXHO
    '60 Mulray Dinghy
    '52 Lyman 15'
    Mercury 150 4-stroke
    68 Outboards representing 11 manufacturers
    Sounds like you suspect the choke. That usually causes black smoke, not white.

    Before looking at that, did you check the condition of the oil?
     
  16. JHornsby3

    JHornsby3 Well-Known Member

    718
    Nov 10, 2020
    Sheridan Oregon
    "Steele'y Tutz"
    1992 300 Sundancer
    Twin 4.3L W/Alpha One Gen II
    I was told that those carbs are very picky. And if there is ever any fuel related issues where the carb is concerned, rebuild it. Also that if any modern fuel(ethanol) is used, rebuild more often. When I took mine in for the rebuild, it showed a lot of corrosion from ethanol use.

    Mercarb on a 92 4.3l

    20210414_173321.jpg 20210414_173347.jpg 20210414_173415.jpg
     
  17. dlows185

    dlows185 New Member

    20
    Nov 3, 2017
    2004 185 Sport 4.3 Mercury
    4.3
    Yes, the oil is the first thing I looked at today. Looks really clean. I then checked to make sure the lead was connected to the choke and then went from there. Doing what I can with the boat off the water for now. I will drag the boat to the river tomorrow (if the wind forecast holds up) and check the operation of the choke and run cleaner through the carb as you stated above.
    I was just curious if I should be getting voltage to the choke with the ignition "ON" Another poster said the power comes from the alt, so ill look tomorrow.
     
  18. GypsmJim

    GypsmJim Active Member

    588
    Aug 8, 2018
    Western New York
    '19 SPX 190 OB, 150 & 5 Mercs
    '17 Whaler 150 Montauk
    '15 Yamaha FXHO
    '60 Mulray Dinghy
    '52 Lyman 15'
    Mercury 150 4-stroke
    68 Outboards representing 11 manufacturers
    In the olden days (leaded gas and later unleaded gas), we rebuilt carbs every few years because they got fouled up.

    Ethanol has a cleaning effect. Since switching to E10 (maybe 25 years ago) I have not had to rebuild a carb yet. (just love that stuff) I have several old boats and a classic car, so its not what somebody told me, its my own personal experience.

    Ethanol deteriorates rubber parts if they are not recent manufacture to withstand ethanol. Water corrodes metal, not alcohol.
     
    rustybronco likes this.
  19. JHornsby3

    JHornsby3 Well-Known Member

    718
    Nov 10, 2020
    Sheridan Oregon
    "Steele'y Tutz"
    1992 300 Sundancer
    Twin 4.3L W/Alpha One Gen II
    True. But the water is held by the ethanol and that is where the corrosion is coming from. The ethanol will trap the water and hold it. And that is one of the reasons it is so bad. It was so bad that I had to buy a used carb to use the both to make one. As for the ethanol being so good for a carb, I disagree to that. Took out three carbs in a Jeep CJ I had and has taken out the carb in an old Jeep XJ I have sitting behind the barn. Same with two lawn mowers sitting out there as well. Not letting them sit is the best cleaning effect on a carb.

    And lets not talk about the reduced mileage caused by the use of ethanol. I would prefer to not have it or any type of bio crap in fuels. The disadvantage far outweighs the advantages.
     
  20. scoflaw

    scoflaw Well-Known Member

    Aug 10, 2011
    cape cod mass, cape coral fl
    1999 Powerquest legend 260 sx
    502 mpi Bravo 1
    Not to turn this into a debate but we in the northeast have had nothing but for the last 30 years. Everything runs just fine.
     

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