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Thread: miller NT225 fuel shutoff problem

  1. #1
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    miller NT225 fuel shutoff problem

    I've researched this site and hope this catches duaneb55's attention.
    I’m working on a Bobcat 225NT with CH20S Kohler engine. When put into storage two years ago, the welder ran like new. During storage, a packrat chewed the wires up on the oil pressure sensor side of the engine that go to a bulkhead connector and on back to the starter switch. I repaired the severed wires with solder and have 100% continuity and insulation. I primed the Keihin carburetor before trying to start it. Time and again it would run until it ran out of prime and quit. I removed the top of the carb with much difficulty and discovered the O rings on the emulsion tube ruined during my prying the top off. The fuel shutoff valve was opening because the float bowl was full.
    The emulsion tube was still plugged even after sitting all night in carb cleaner. I had to drill the obstruction out of the emulsion tube and replace the torn O rings. When I reinstalled the carb and tried to start it, it would start without priming but almost as quickly shut down. I checked the fuel shutoff circuit for voltage, and discovered the only time it got current was while being cranked. As soon as the starter switch was released to the run position, the circuit tester light would go out. I hot wired the fuel shutoff valve to the battery and it would run all day, but wouldn't slow down to idle when the switch was placed on that position nor would it shutdown unless I removed power to the fuel shutoff valve.
    I suspected the low oil pressure shutdown might be at fault and checked the two prong sensor. It is NO but closes as soon as the engine starts. I further figured the only signal it could send would be ground, because there is only the single yellow wire going to the two prong sensor. I grounded the yellow wire and blew the 30 amp fuse coming off the starter upon turning the switch on. I then further reckoned it might originally have had a hot wire going to the other prong on the sensor which the packrat removed entirely. I jumpered 12v to the yellow wire and it made no difference. The fuel shutoff valve still loses voltage as soon as the starter switch is released.
    I can’t figure how that low oil pressure shutdown works. It makes no sense to me having the switch close internally with nothing connected to the other side. But all the 3 wiring diagrams I was able to download from Kohler show only one wire going to that sensor. However, one of the diagrams show a ground symbol at the bottom of the sensor. I fear I’m looking at the wrong diagrams. Anyone got any ideas where I might start on this thing? Are you supposed to see daylight through that emulsion tube? I drilled it from the bottom and felt I was drilling through what may have been an intended partition above the bottom-most ports before it drilled through. I’m unable to find anyone to sell me a new one. Any advice on this will be appreciated. I fear shop repair costs would scrap this otherwise clean, low hour welder.
    Last edited by croper; 04-24-2015 at 12:07 PM. Reason: didn't name carburetor

  2. #2
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    Re: miller NT225 fuel shutoff problem

    @ zapster - Move to general welding, or the Miller forum for more views. I messaged duaneb55 for you to check this thread out. I don't have any insight on this issue.

  3. #3
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    Re: miller NT225 fuel shutoff problem

    Quote Originally Posted by AndrewDavenport89 View Post
    @ zapster - Move to general welding, or the Miller forum for more views. I messaged duaneb55 for you to check this thread out. I don't have any insight on this issue.
    thanks

  4. #4
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    Re: miller NT225 fuel shutoff problem

    Thanks for the heads up Andrew.


    Welcome to the forum croper.

    The O/P switch - as you've discovered - is controlling battery + voltage to the RUN circuit and not battery ground.

    Just so we can make sure we're looking at the same machine wiring diagram we need the unit SN off the data tag located on the faceplate. Your machine's specific diagram should be affixed to the inside of one of the side panels if you haven't discovered this already. If you don't have a manual, you can go here http://www.millerwelds.com/service/o...uals.php?model, enter the SN or select by model name and download the operator's manual.

    I'm afraid I can't answer your question on the carburetor but get the correct wiring diagram to review, post the SN and we can go from there.
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  5. #5
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    Re: miller NT225 fuel shutoff problem

    Quote Originally Posted by duaneb55 View Post
    Thanks for the heads up Andrew.


    Welcome to the forum croper.

    The O/P switch - as you've discovered - is controlling battery + voltage to the RUN circuit and not battery ground.

    Just so we can make sure we're looking at the same machine wiring diagram we need the unit SN off the data tag located on the faceplate. Your machine's specific diagram should be affixed to the inside of one of the side panels if you haven't discovered this already. If you don't have a manual, you can go here http://www.millerwelds.com/service/o...uals.php?model, enter the SN or select by model name and download the operator's manual.

    I'm afraid I can't answer your question on the carburetor but get the correct wiring diagram to review, post the SN and we can go from there.
    Thanks to you, I can see a light at the end of the tunnel. Much appreciation, Charlie Roper

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