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Old 06-06-2024, 09:02 AM   #1
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Default Idling issue #2

Hi Guys

I have a new carburetor on a 3ltr (Maxum 1800), the recommended tick over is 700rpm (from the engine manual)
With a cold start, tick-over is 550/600 and the engine won't run at this speed so requires a touch of throttle, when we come back (engine up to temperature), neutral (no throttle) tick-over is the perfect 700/750.
Is this a slow speed jet adjustment that is needed, which will get the cold tick-over (without the extra throttle) to the 700/750 region.

Regards: John
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Old 06-06-2024, 11:43 AM   #2
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I don’t think that marine carburetors have a high speed idle adjustment screw like the automobile ones did. It’s fairly common to have to provide some throttle when starting a cold engine to keep it running but only for a minute or two.
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Old 06-06-2024, 07:04 PM   #3
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Hi Mike

Thank you for your prompt reply: I don't think the carburettor has a 'high speed idle adjustment screw' nothing in the service manual (page: 5B-16/17) shows or lists such a adjustment screw, and I'm not going to touch anything with 'high speed' annotated to it, she purrs along at WOT, giving a smooth 5000+ revs
Your second point regarding cold starting, while I agree with you, a bit of throttle to get the engine going may be needed, especially in less than temperate climes, but never is it or should it be required to maintain a tick over, all the carburettor engined vehicles I have started has never required me to keep my foot on the throttle to maintain the idle, the manual or automatic choke looks after that, a engine fitted in a boat should be no difference, after all the engine doesn't know its in a boat.

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Old 06-06-2024, 07:46 PM   #4
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Hi John, you are correct in what you have said. The only thing on the carburetor that knows whether the engine is cold or hot is the automatic choke. Have you verified that it’s fully opening in a few minutes from a cold start? Low speed circuit in the carburetor is the same cold or hot. Another thought is could the throttle sticking when warmed up giving you the higher idle which happens to be at the desired rpm? What happens if you disconnect the throttle cable from the carburetor when the engine is warmed up?
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Old 06-07-2024, 07:56 AM   #5
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Good point, the automatic choke is worth checking, plus the throttle connections.

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