merc 3.0 carb low speed idle setup.

Fscott4

Petty Officer 3rd Class
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Sep 8, 2022
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3.0 liter mercruiser, yesterday the carb started flooding badly while on the water. I disassembled the carb in the boat and seem to have fixed the problem but the gasket got torn and I am going to rebuild it. My question is the initial setting for the low speed idle. I will be setting it up on the water under load but I would like to be at least in the ballpark. Also wondering what this engine should idle at in the water, Ive seen 750, 850 etc.
Thanks!
 

alldodge

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Which 3.0 like a serial number?
Figuring maybe a Merc carb but could be a 2GC, TKS
 

Scott Danforth

Grumpy Vintage Moderator still playing with boats
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Start about 3/4 out from seated on the idle mix. The rebuild kit will have instructions
 

markhodges78

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Aug 4, 2016
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I would say if you haven't touched the low speed idle jet then count the turns in and put it back where it is and then adjust from there.. the recommended setting is just a starting point to get it running
 

Fscott4

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I did mess with the screw when we were on the water and of course I lost track of the original position while disassembling the carb 3 times on the water :)
 

markhodges78

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I did mess with the screw when we were on the water and of course I lost track of the original position while disassembling the carb 3 times on the water :)
The way I would do it is on the water set it to 1 1/4 turns out start the boat (the boat will start where ever you set the idle mixture to it just may not idle very good)
Set the idling as low as you can and still keep the boat running. start backing out on the idle mixture a little at a time the engine will most likely idle up. adjust your idle speed back down as low as you can without the engine shutting off the continue to turn out the idle mixture. go back and forth until the engine starts to stumble then turn it back in until it stumbles now put it half way between the stumble points and adjust idling to specs
the object is to have the throttle plates closed as much as possible to allow engine to run on the idle circuit
 

Fscott4

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Sep 8, 2022
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I am gonna give that a try this am. Carb rebuilt and run on baffles so now to the water for a tune under load.
 
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