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Old 08-19-2019, 06:34 PM   #1
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Default Black smoke

I have a 3300scr with twin 5.7 mer engines and brovo 2 outdrives i have large black smoke at start up in both engines and a gas spill in the water i was told it was un burnt fuel has anyone come across this or give any advise as to what the cause may be and both carbs have been rebuilt thanks
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Old 08-19-2019, 09:26 PM   #2
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Black smoke is unburdened fuel. Are the engines hard to start? Sounds like the carbs are dripping fuel after shut down.
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Old 08-19-2019, 11:11 PM   #3
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Default Smoke

No thats what i dont understand they start really good and idle good and runs great but there is this black smoke and the slick when they are running not even a bit of hesitation. I just bought the boat a while back and previous own advised that the carbs had been rebuilt im at a loss
Thanks for your reply. Im open to trying anything.
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Old 08-19-2019, 11:55 PM   #4
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Does the smoke clear quickly? Or do they smoke until up to temp?
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Old 08-20-2019, 01:51 AM   #5
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From the description of smoking when first starting I would think blue smoke being oil from leaking valve seal and worn guides. Have you pulled the spark plugs to see how they look?
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Old 08-20-2019, 10:58 AM   #6
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No they keep smoking but dose get a little netter
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Old 08-20-2019, 10:59 AM   #7
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Its not blue smoke deffinatley black
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Old 08-20-2019, 11:13 AM   #8
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No they keep smoking but not as bad but always the slick
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Old 08-20-2019, 11:33 AM   #9
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Have you verified the choke plates are opening all the way? If the carbs were rebuilt their not adjusted properly.
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Old 08-20-2019, 11:58 AM   #10
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Yes they are thanks i appreciate all the analysiskeep them coming need to find the problem
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Old 08-20-2019, 03:35 PM   #11
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What carbs; 2 bbl vs 4 bbl, Mercruiser vs Quaderjet vs Weber, ...
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Old 08-20-2019, 08:08 PM   #12
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Two barrel
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Old 08-21-2019, 10:01 AM   #13
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I would suspect the carb rebuild was sketchy. Wrong float level adjustment/stuck float will cause the symptoms you describe.
Same with a saturated poly float or a brass one that has a pinhole.

At idle, with flame arrest or off, do you see any fuel bubbling out the breather tube?
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