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Old 06-27-2019, 10:14 PM   #1
Lt. JG
 
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Default Merc 5.0 2BBL carbed stalling after 20 minutes

Quick problem/ question. Have an 01 maxum with a 5.0 merc carbed. On the Water for 30 minutes, everything was fine. Then it felt like the motor just shut off, bogged out and died. Started right back up, runs good for a few minutes then the idle drops and it stalls. You can see the idle drop to like 300 then back up to 800 once or twice then it just dies. Starts right back up and same thing over and over.

Since this happened at the end of last season we have replaced:
Spark plugs
Wires
Ignition Coil
Carburator
Fuel Pump
Fuel / Water Seperators (2)
Replaced distributor cap last season.

Things to check tomorrow:
Fuel tank vent (I can see vapors coming out the side of the boat when filling gas though)
Exhaust manifolds (no clue how to check this)

Any other ideas or suggestions?
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Old 06-27-2019, 10:47 PM   #2
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Does this occur only at idle, or do you get these symptoms under power?
Are the plugs wet or dry after this happens? If wet then likely a flooding issue caused by carb needle or float.
If occurs at idle only, you may just need to adjust the idle, and idle mixture screw.
I recommend you download service manual 24 from documents and see "carburetor malfunctions". For adjusting idle mixture screw, see pg 4B5- Timing follow steps 3-8.
If this is occurring at power then likely a carb or fuel issue.
Have you ever had the carb rebuilt?
Are you sure that your gas is good, no water?
Why did you replace the water separator twice?
To check the manifolds you will need to remove them. You will need a manifold gasket. Let us know if you want to do this and we can give you some pointers. Not hard, just heavy.
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Old 06-27-2019, 11:39 PM   #3
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OP says he replaced the carb.

Don
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Old 06-28-2019, 12:15 AM   #4
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The two most common time related issues are bad coil and clogged fuel tank vent. Next time it happens remove fuel cap and see if it stays running. new parts could be faulty, happens. Cap, coil and carb.

When it happens check for spark and fuel.
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