3.0 low speed help

[Badfish888]

So if no one knows already. I have a 98' 175 with the 3.0.
I have replaced the following Since last week.
cap and rotor, plugs, timing cover, new fuel lines and new filters.
And run only premium fuel.

te boat refuses to idle when hot. When we first get to the ramp it will fire right up and idle (kinda) smooth. Ran it for 2 hours today at cruising speed. Came down to clutch fwd Andit stumbles and wants to die. Anything above idle ad it will get smoother and smoother. Ive adjusted the mix screw any less it dies Any more it runs rough. Adjusted the speed screw on throttle cam Any less it dies Any more and im just slamming my lower in and out of gear. Timing same deal. Any farther advanced it runs like **** And farther retarded it wont run. Carb has been completely rebuilt with new everything. The only thing i havent dine is a valve adjustment

 

[dvx216]

As much as you will not like the sounds of this I would go through the carb again and check the idle jets.You said it will not run when its hot because when it warmed up the choke is not in play the choke increases the draft in a cold carb to helps it run rich or get a little more fuel to the cold motor.One thing you can do if you haven't is once it is all warmed up and idling bad apply the choke to see if that smooths it out.But before I would do any thing I would tap the fuel line before the carb and check your idle fuel pressure it might be low at an idle which is signs of a weak fuel pump. Auto zone has a rental kit to do this. Search mercruiser service bulletin 97-8 it will give you a step by step check off list

 

[Badfish888]

I deff agree that is fuel, but if I had a weak fuel pump, wouldn't it run bad all the time. Not just when it's hot? And the only thing I can really think about the carb is the float adjustment. I say this because I could never get it quite right. And I only had to make minor adjustments when I installed the new one? Is that normal. And when you say check the jets do you mean take it apart and clean again. Other than warm engine idle speed. It runs great.

 

[Docsteder]

It could be "dumping", the carb, that is. When the engine is warm, look down the carb for dripping fuel aka "dumping" . If this is happening, you either have dirt stuck in the needle & seat or your float is adjusted incorrectly. The only way to fix this is to take the carb apart and clean out the needle & seat and check the float height per the rebuild instructions.


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