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Old 13-05-2022, 14:33   #1
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Yanmar 3GM30F hard starting

I have a 3GM30F in our 2002 Beneteau 331. It isn't starting as readily as I think it should.
Our start procedure has been 3/4 throttle, and crank. It takes around 5-6 seconds to start firing. (I think it should be less)
We just had the injectors rebuilt and that seems to have helped somewhat in that there is not as much of an obnoxious cloud of black smoke upon starting. ( the rebuild folks said the spray pattern was a hose)
I've tried starting with the fuel shut off for a couple seconds while cranking, and then pushing the shutoff in. I think that may be helping, but have only tried it a couple of times.
any ideas out there?
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Old 13-05-2022, 16:25   #2
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Re: Yanmar 3GM30F hard starting

What is the ambient temperature? This has a significant effect on starting time when below 50F (10C).

Have you confirmed it isn't an electrical issue (e.g. low starting rpm)?

To confirm the electrical aspects, try starting using the decompression levers. If this improves the staring time, you have an electrical problem.

Method -

1. decompress all cylinders
2. spin the engine over using starter motor for 5+ seconds while decompressed
3. with starter motor still engaged, re-compress one cylinder.
4. if it fires quickly, compress the other two cylinders sequentially.

If the start time after re-compressing is significantly reduced, you have an electrical problem which is causing low starting rpm.

If the start time remains unchanged, you have a fuel or air problem.
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Old 13-05-2022, 16:43   #3
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Re: Yanmar 3GM30F hard starting

You may have a small fuel leak which is letting air into the fuel system. Would create the slow/hard start issue you are having.
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Old 13-05-2022, 17:17   #4
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Re: Yanmar 3GM30F hard starting

Most common reason for slow starting is electrical. Ie. Battery condition, battery leads, worn starter motor, faulty glow plugs etc.

Mechanically, you have done the injectors so next step would be a compression test.
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Old 13-05-2022, 17:36   #5
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Re: Yanmar 3GM30F hard starting

My '02 3GM30F starts so quick I can't get my finger off the start button fast enough, and with throttle at idle. I'd guess fuel.
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Old 13-05-2022, 18:28   #6
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Re: Yanmar 3GM30F hard starting

How old is the fuel?
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Old 13-05-2022, 18:46   #7
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Re: Yanmar 3GM30F hard starting

I've had mine slow starting in coldish weather. I read here on cruisers forum somewhere to start with full throttle, something was mentioned that full throttle changes fuel timing or something...

Anyways, it makes all the difference in the world! Full throttle, then quickly lower the gas as it starts. With this method it starts very quickly warm or cold.
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Old 13-05-2022, 21:21   #8
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Re: Yanmar 3GM30F hard starting

As stated above in several posts look at electrical.
Starting with fully charged battery may be the difference.
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