Full throttle needed to start Yanmar 2GM20F - Page 3 - SailNet Community
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post #21 of 25 Old 12-20-2012
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Re: Full throttle needed to start Yanmar 2GM20F

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Originally Posted by 73Morgan View Post
Ran some tests, cranking and playing with the decompression lever with a cold engine does not feel like it changes anything, it only feels like the compression builds up after the engine warms up. This just might be explaining the hard start problem.
You should notice a distinct change in cranking speed between 'compression on' and 'compression off'... you'll also 'see' the engine shaking harder with the compression lever released as the starter tries to drive the engine through the compression phase.

If you're not noticing a difference, that's definitely something to look further into.

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post #22 of 25 Old 12-20-2012
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Re: Full throttle needed to start Yanmar 2GM20F

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Originally Posted by 73Morgan View Post
If your engine was built after 1997 that might explain the difference. My manual covers the 1, 2 & 3GM models.
Normal start positing is at medium speed.
The exception is starting in cold weather the throttle should be in high speed with the decompression handle in the decompression position, start cranking and push the lever to the compression position, after it starts pull back to medium speed. There seems to be a conflict because there is a "caution" which states to pull back to idle immediately when the engine is started at high speed. We all know you should not rev a cold engine any more than necessary . The injection timing being delayed at high speed is also there.

I would actually be happy if the engine started right away on a 80 degree day, and came right back to idle without stalling.
Two things are happening when the decompression levers are placed in the decompression position..one..when the engine is turning over you are lubing the engine parts. Second..provided you are at the same time holding in the 'kill' or fuel cut off lever..thus clearing out any fuel in the pre combustion chambers and cylinders.

Once those procedures are accomplished while the engine is still turning over via the starter..release the decompression levers and the fuel cut off lever...
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post #23 of 25 Old 12-25-2012
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Re: Full throttle needed to start Yanmar 2GM20F

MarkSF :

Am I correct in thinking that the Yanmar doesn't have glow plugs? I'd expect this to result in difficult starting and having to use full throttle to start. Can't understand why they thought it would be OK to not install them.

Sometimes it is best not to have starting aids. I am wary of glow plugs on a marine diesel. If they stop working, the motor will be helluva difficult to start. I am unconvinced that they are worth the risk.

The older motors don't need them if the compression is good.
.

Last edited by Rockter; 12-25-2012 at 05:00 PM.
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post #24 of 25 Old 09-22-2019
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Yanmar 2gm; I've always needed full throttle to start cold. Then lots of black smoke for a few seconds then at warm up all os good.
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post #25 of 25 Old 09-22-2019
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Re: Full throttle needed to start Yanmar 2GM20F

Years ago i had a 1 lunger yanmar that wanted full throttle at start. Per factory
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