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Old 05-25-2023, 08:07 PM   #1
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Default Mercruiser 3.0 bogging down on throttle.

After winter storage and launching, my engine (Mercruiser 3.0 1994) starts fine but dies on gas.

Haven't had any trouble before.
What I tried is to give as much gas as possible without it dying and then rev the engine by manually giving gas via the carburetor's throttle. (Filter removed)
The engine then revs nicely and sounds as it should.

The conclusion I draw is that the engine is getting both fuel and air as it should and that it is not the fuel that is at fault.
Shouldn't be the fuel pump either, as the carburettor rotates nicely when opening/closing the throttle.

Is it the throttle that is haunting/stifling faith?
Thanks for the answers and thoughts on this.
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Old 05-25-2023, 11:29 PM   #2
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Need so clarification. The engine starts and idles fine; correct? The engine will accelerate fine when in neutral; correct? The engine doesn’t accelerate fine when in gear; correct?

If all these are correct you could still have a fuel issue as in neutral there is no load on the engine so it doesn’t take much energy to increase rpms. I once had a boat with a V6 that had a dead cylinder and only under load in the water could you tell the difference. Have you checked the inside of the distributor cap for corrosion?
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Old 05-26-2023, 06:22 AM   #3
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No it has the same issue in neutral and with gear.
The difference is that i can make it run high rpm by opening and closing the carb by hand, not from the gashandle.
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Old 05-26-2023, 03:21 PM   #4
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Down by the boat now and tested it after cleanig carb filter and ignotion house.
My choke plate stays Open all the time, even after giving it throtle. It should close by vacuum right?
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Old 05-26-2023, 06:21 PM   #5
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Quote:
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Down by the boat now and tested it after cleanig carb filter and ignotion house.
My choke plate stays Open all the time, even after giving it throtle. It should close by vacuum right?
Your engine should have an electric choke. If you post a picture of the carburetor I can verify. There should be a round disk on one side. You can loosen the screws and rotate the disk to see if the plate moves.
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Old 05-26-2023, 06:26 PM   #6
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Yes Thats correct. It opens after 2-4min full but shouldnt choke close When i Give it gas?
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Old 05-26-2023, 10:33 PM   #7
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Quote:
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Yes Thats correct. It opens after 2-4min full but shouldnt choke close When i Give it gas?
The choke should close when the engine is cold and you move the throttle initially. It should then open in a few minutes once the engine is running. If the engine is warmed up the choke should not close.
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Old 05-28-2023, 11:32 AM   #8
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When I have the engine in neutral and give it throttle so that the engine revs just to the point where it doesn't start to fuss via the throttle and then rev the engine by opening and closing the choke by hand with the flame arrestor removed the engine revs just fine.
Bogging or hasitation.
Is this a clue about what it can and cannot be?
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Old 05-28-2023, 12:00 PM   #9
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Under Documents of this site is Mercruiser manual #26 for your engine. Try following the instructions for adjusting the choke to see if that helps.
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Old 05-28-2023, 06:37 PM   #10
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After adjusting the carburettor today, I can now rev the engine properly BUT only after I disconnect the choke and the choke is almost fully closed. (Can't start cold like that)

Something here I don't quite understand.
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Old 05-28-2023, 07:55 PM   #11
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If the engine will only run with the choke closed then the carburetor is adjusted to lean.
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Old 06-06-2023, 01:31 PM   #12
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I ended up starting the engine via external tank first to rule out the fuel going bad.

Then I checked that fuel was flowing properly to the carburettor by removing the flame guard and disconnecting the throttle cable so I could throttle and check the carburettor itself.

Ended up taking the carburetor off, took it apart at home and cleaned every little hole with wire, needle, toothbrush and crc carburetor spray.
Now it works fine again.

It should be pointed out that the carburettor gave up during winter storage outside, something that was not noticed during the last trips in the autumn.
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Old 06-06-2023, 06:19 PM   #13
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Hopefully you can enjoy the rest of the season trouble free.
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