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Old 16-06-2017, 12:37   #1
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Yanmar3gm30f - Idle adjustment

I need to adjust the idle RPM on our Yanmar3gm30f.


Has anyone got an explanation, guide or link to how this is done ?
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Old 16-06-2017, 13:29   #2
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Re: Yanmar3gm30f - Idle adjustment

I think this is adjusted through the throttle cable. IIRC, this is an easy fix at the front top of the engine at the lever where the cable comes in. (That's clear as mud, but I'm not looking at the engine right now and my memory of these things suck.)
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Old 16-06-2017, 17:54   #3
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Re: Yanmar3gm30f - Idle adjustment

Gamayun is correct. At the lever on the injector pump, where the cable connects. There is a threaded stop bolt. Loosen the lock nut and screw the bolt in while the engine idles. Tighten lock nut.

Literally the first maintenance item performed when I bought my boat seven years ago.
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Old 16-06-2017, 18:05   #4
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Re: Yanmar3gm30f - Idle adjustment

BTW, if you Google yanmar 3gm30f service manual, you can find a PDF to download.
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Old 16-06-2017, 18:07   #5
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Re: Yanmar3gm30f - Idle adjustment

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Originally Posted by carlager View Post
I need to adjust the idle RPM on our Yanmar3gm30f.


Has anyone got an explanation, guide or link to how this is done ?
Correct idle speed is in the range 825-875 rpm.

Examine your engine. You likely have two possible ways to adjust the engine speed: (1) adjust the play in push-pull cable to the remote control engine control; or (2) adjust the idle adjustment screw. #1 is usually to be preferred.

Start the engine with transmission in neutral and remote engine control advanced.

Run the engine until it reaches operating temperature

Make sure you have no loose items (hair, clothing) that might be caught by moving parts of the engine.

Adjust the play in the push-pull cable. Or adjust the idle adjustment screw.
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Old 16-06-2017, 18:20   #6
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Re: Yanmar3gm30f - Idle adjustment

Respectfully, Alan, your number one would be a cable adjustment, not idle adjustment.

However, If one miss adjusts the cable it will raise the idle.

Number two is best.
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Old 17-06-2017, 02:16   #7
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Yanmar3gm30f - Idle adjustment

Thanx a lot. Why does the Engine have to reach normal operating temperature before the adjustment ?
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Old 18-06-2017, 15:26   #8
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Re: Yanmar3gm30f - Idle adjustment

Well, specifically I don't know. To speculate, I'd say it's because that is the state the engine operates in at all times. Except the few minutes during warm-up. The engines works at normal operating temp and that's where it needs to idle to spec.

Every manual I've ever read says adjust idle speed, or mixture on gas engines, at operating temp.

I'll leave it to someone else to talk about expansion rates of various metals, and tolerances, clearances and what not.
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Old 18-06-2017, 22:09   #9
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Re: Yanmar3gm30f - Idle adjustment

Hi

Mostly so your combustion is stable, parasitic drag on the rotating components is stable as the lubricants and drive belts are at operating temperature, and mechanical clearances are where they will be when the engine is running.

Cold engines do idle at slightly lower speeds than warm ones as a rule for the abovementioned reasons.

Cheers Tom
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Old 18-06-2017, 23:12   #10
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Re: Yanmar3gm30f - Idle adjustment

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Respectfully, Alan, your number one would be a cable adjustment, not idle adjustment.

However, If one miss adjusts the cable it will raise the idle.

Number two is best.
1. Yes, I think you are right, four winds. Probably.

When I nominated checking and adjusting the play in the push-pull cable as the adjustment to make, I was assuming that the idle adjustment screw was set correctly and that age-related issues in the push-pull cable were affecting the engine idle. The two settings - the idle screw and the setting of the push-pull cable - interact (or can interact).

2. To attempt to answer carlager's question about why idle speed is defined as the speed of warm idle for a diesel engine:

Some diesel engines with sophisticated electronic controls have two idle speeds: a warm idle; and a cold idle speed. The cold idle speed is always higher than the warm idle speed.

Nineteen is correct. One way of defining warm idle speed for a diesel engine is as the minimum engine speed that maintains desired oil pressure (and so on) in a sustainable/stable way.

Yanmar 3GM30F engines, similar to many other small diesel engines, do not have a sophisticated control setting cold idle speed. You have to that yourself by advancing the remote engine control before start up, so that the engine runs at about 1200 rpm.

Once the engine is at operational temperature, 1200 rpm is too high for no-load idle (or even for loaded idle, the sort of engine speed you might want when motoring into a dock, with the transmission in gear and the engine just ticking over).

So the manual defines idle speed as 850-875 rpm, which is just right for no load idle and which gives an engine speed of around 900 for loaded tick-over without lugging.
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Old 19-06-2017, 11:16   #11
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Re: Yanmar3gm30f - Idle adjustment

Ah, I see where your coming from, Alan. Certainly the cable adjustment changes over time from wear and maybe contamination.

I guess the basic idea is to maintain some slack/freeplay in the cable at idle position, so the idle stop adjustment ensures the correct idle speed.

Smart money is on checking both any time it needs fiddled with.
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