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Go Back   SailNet Community > On Board > Gear & Maintenance > Engines > Diesel
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Diesel This is a new forum dedicated to diesel engines and their applicable accessories.


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Old 05-15-2012
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Yanmar yms12 wont idle

Help, I just refurbished (cleaned like new) the fuel tank, replaced the filters, bench tested the fuel pump...works. No leaks that I can detect. Cranks like a jem at 1/4 throttle, to keep it running I have to rev it a little and can back it to 1/4 - 1/2 throttle and will purr but any lower it chokes out. Checked to make sure choke is open but still wont idle. ideas?
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Old 05-15-2012
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Re: Yanmar yms12 wont idle

At what RPM does it stall? There is an adjustment on the throttle linkage of most diesels to set the idle speed. Note that diesels don't have a choke.
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Re: Yanmar yms12 wont idle

I have no rpm gauge but if a idling motor runs at 600rpm and full throttle is around 3500 I would say it chokes out (for lack of better words) at about 1000-1200 rpm, ALMOST slow but above idle. If I catch it I can give full throttle and keep it running, if im late it dies with a chug.
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that's not a choke

Make sure the fuel shut off is not engaged and the cable moves freely. Sounds like it is not getting enough fuel.
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Old 05-16-2012
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Re: Yanmar yms12 wont idle

Does sound like the fuel is getting cut off early if it indeed won't run below 1000-1200 RPM. Is your engine stop a separate control or engaged by moving the throttle past idle? If the the latter, it could just be a simple adjustment or a sticking cable like KBuckley suggests.
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Re: Yanmar yms12 wont idle

due to a broken choke cable I am hopping from cabin to cockpit to adjust the choke and hit the engine kill lever.

Could it be my fuel pump, when I took it off I bench tested it and got a good flow by pumping the lever with no sign of leakage.

Another note, before cleaning the fuel tank it did idel, like a charm actually, but did not like going into higher rpm's. Maybe this will help.
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Re: Yanmar yms12 wont idle

also, if I put an electric fuel pump inline before the fuel filters, would it blow the diaphragm out of the manual fuel pump or should I bypass the manual fuel pump all together? Just an idea, I would really rather fix it then throw money at it.
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Old 05-16-2012
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Re: Yanmar yms12 wont idle

A diesel with a choke? Did you find all the air bleeders? Sometimes they are not easy to find. Bleed the injectors right at the banjo fittings if all else fails.
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Re: Yanmar yms12 wont idle

Quote:
Originally Posted by Domknotty View Post
due to a broken choke cable I am hopping from cabin to cockpit to adjust the choke and hit the engine kill lever.

Could it be my fuel pump, when I took it off I bench tested it and got a good flow by pumping the lever with no sign of leakage.

Another note, before cleaning the fuel tank it did idel, like a charm actually, but did not like going into higher rpm's. Maybe this will help.
If it didn't pull max RPM's under load before could be dirty or over pitched prop? Maybe a clogged vent? or fuel pickup tube screen in the tank? No idle after cleaning, maybe some debris broken loose and partially blocking passages somewhere? could be hard to find. Air leak somewhere? A pressure pump would probably show where:


The Diesel Page, Electric Lift Pump and Racor Filter installation

Try disconnecting all the control cables and manually open throttle
Check all connections, make sure there is no air spaces in filters.
You could by-pass the tank with a seperate fuel source?
It appears that something happened after you cleaned the tank?
If all else fails you might take the pump/governor assembly to a shop for cleaning and re-calibrating. If so make a mark on the block and pump housing for easy re-install. Let us know what you find.

Paul T
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Re: Yanmar yms12 wont idle

Please describe what you are calling the "choke". There should not be a choke on a diesel....

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