Miller Bobcat 225NT issues
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  1. #1
    Join Date
    Jan 2017
    Location
    Houston Texas
    Posts
    12

    Miller Bobcat 225NT issues

    Hello,

    I have a Miller Bobcat 225NT that I have owned for about 5 years, the last 2 or so I had it lent to a friend to do some repairs at his church (welding down grates and what not to prevent theft from metal mites) and I just got it back 3 weeks ago to go down to my moms house in Rockport to run auxiliary power after the hurricane.

    When I got it back, the vacuum fuel pump had been replaced with an electric pump, there was no auxiliary or welding voltage and it would die at low idle/takes for ever to stop running when moved to the off position.

    The electric pump was wired in off the main switch and it only pumps in the start, high idle and high/low idle. Wire is just wrapped around a terminal.

    For the lack of voltage I didn't have much time to take many diagnostic readings before leaving to go down from Houston to Rockport, so I started cleaning all of the electrical connections and slip rings. Fuse 1 is good. I did not confirm fuse 2 was good or not.

    I was able to get auxiliary voltage back (120 and 240) and had 55 volts of OCV at the welding lugs (did not strike an arc to test and I don't remember what the selector switch was on, but it was filthy in there) and it ran over 24 hours providing auxiliary power down there while patching roofs, clearing downed trees and cleaning up.

    Things are settling down and I would like to sort out the idle/stop issue and fuel pump.

    Serial number KH357108
    Stock number 903517
    Kohler engine
    Machine has 24XX hours on it

    The idle issue is the low idle, it will slowly come down in engine speed and then die (no loads being applied). The solenoid appears to be moving while it is running.

    These pictures are taken with the air cleaner assembly removed.
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    The stop issue is when the start switch is moved to off, it takes at least 30 seconds to go from high idle to off. It does go through the cycle of speeding up right before shutting off. This is much longer then I ever remember.

    Would both of these functions be controlled by PC1?

    For the fuel pump this is where I should tie into it correct?

    Thanks and this forum has been a great resource.

    Peter
    Attached Images Attached Images   

  2. #2
    Join Date
    Mar 2009
    Posts
    3,304

    Re: Miller Bobcat 225NT issues

    Why even fool with the electric pump? Yank all that junk off and figure out why the vacuum operated pump (supposedly) stopped working in the first place.

    And no "friend" of mine would ever use this welder again and sure as heck wouldn't have backyard engineered it to begin with.
    "You can't out puke a buzzard"

  3. #3
    Join Date
    Feb 2005
    Location
    Louisiana
    Posts
    1,923

    Re: Miller Bobcat 225NT issues

    Quote Originally Posted by Pipeliner View Post
    Why even fool with the electric pump? Yank all that junk off and figure out why the vacuum operated pump (supposedly) stopped working in the first place.

    And no "friend" of mine would ever use this welder again and sure as heck wouldn't have backyard engineered it to begin with.
    ^^^^^^^^^^^^^^^^^^^^^^
    This!

  4. #4
    Join Date
    Jan 2017
    Location
    Houston Texas
    Posts
    12

    Re: Miller Bobcat 225NT issues

    I am not upset about the change, he meant well. What would happen with the vacuum pump is it would dry out from lack of use and you either had to crank forever or dribble some gas down into the line from the carburetor end to prime it. The vacuum pump is gone so I would have to purchase that, its probably cheap, but the I believe the easier task is a proper electrical connection at this point, unless of course this is the source of the machine not shutting down properly.

    Thanks,

    Peter

  5. #5
    Join Date
    Apr 2017
    Posts
    401

    Re: Miller Bobcat 225NT issues

    Electric fuel pumps have different pressures and volumes ,the engine on your Bobcat works on very low fuel pressure.
    The Bobcat had a electric fuel pump option however the pump used has rated for the engine used. Not just any electric fuel pump will work without flooding or a host of other problems.
    Really the pulse pump is your best option , yes if it sets it takes a little longer to push fuel but over all its your best option.
    Electric fuel pumps on welders need to be set up as to not pump fuel when the ignition is on but engine off, I have seen engine drive fires because of this.
    Some are set up to pump fuel during starting and then switch to a engine normally open oil pressure switch to remain energized when engine running.
    Regardless of what PC-1 is doing your engine drive should shut off the minute you turn the ign switch (S-2) to the off position.
    It should never continue to run after S-1 is switched to the off position.
    You need to check for anything that is back feeding power or any wiring changes that may have been made however I tend to think you may have a problem with S-2 sticking maybe???

  6. #6
    Join Date
    Jun 2012
    Location
    Bemidji MN
    Posts
    13,563

    Re: Miller Bobcat 225NT issues

    Quote Originally Posted by Dana gear View Post
    Really the pulse pump is your best option , yes if it sets it takes a little longer to push fuel but over all its your best option.
    Mine cranks for quite a while after sitting for a few weeks. Was wondering if that was normal or a sign the pump was going.
    Dave J.

    Beware of false knowledge; it is more dangerous than ignorance. ~George Bernard Shaw~

    Airco 300 - Syncro 350
    Invertec v250-s
    Thermal Arc 161 and 300
    MM210
    Dialarc
    Tried being normal once, didn't take....I think it was a Tuesday.

  7. #7
    Join Date
    Jan 2017
    Location
    Houston Texas
    Posts
    12

    Re: Miller Bobcat 225NT issues

    Dana Gear,

    The electric pump on it states 4 PSI from memory, I'll check it.

    I agree on the wiring you only want it on when the engine is running.

    I went a head and ordered a pulse pump it was sub $10.

    Have you ever heard of a check valve being placed before a pulse pump to keep it primed?

    Thanks for the input.

    Peter

    On the S-2 sticking, I'll pull it off and see if it continues to feed power when it is rotated through the different positions.

  8. #8
    Join Date
    Apr 2017
    Posts
    401

    Re: Miller Bobcat 225NT issues

    4 psi would be the maximum pressure for that carburetor to see in operation.
    Yes I have seen check valves however its not that fuel is reverse flowing generally after sitting for a week or so the fuel evaps in the carb another area fuel is lost is when the engine dive bounces around a lot like on a trailer on a bad road ,fuel can actually slosh out into the intake manifold a little.
    Honda had a problem with this on engines used on service trucks, mostly air compressors and recommended that you turn off the fuel and let the engine die as fuel was sloshing into the cylinder and washing off the oil on the cylinder wall and in turn passing the rings and into the crankcase, overtime the engine oil would be diluted by fuel.

    Most all pulse pumps require a little cranking action after setting for a time and no this is not a indicator of a bad pump, they did it when they were new.

  9. #9
    Join Date
    Jan 2017
    Location
    Houston Texas
    Posts
    12

    Re: Miller Bobcat 225NT issues

    Sorry I have been gone for a while.

    I did two things changed the plugs and cleaned the back of the ignition switch. Not sure which was causing the issue but it idles down like it suppose to be and it takes about 20 seconds to turn off from when it is switched off.

    I have not changed out the electric pump to the pulse pump yet.

    Here are pictures of the back of the switch.

  10. #10
    Join Date
    Jan 2017
    Location
    Houston Texas
    Posts
    12

    Re: Miller Bobcat 225NT issues

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  11. #11
    Join Date
    Apr 2017
    Posts
    401

    Re: Miller Bobcat 225NT issues

    Definitely looks like the ignition switch was gotten hot internally, could be a internal short.
    You can test it. In your bottom picture facing out.
    Top left terminal is start.
    Top right terminal is battery.
    Middle right terminal is run/idle.
    Bottom middle terminal is Run.
    When switched to off position there should be no power to many other terminals only the battery terminal should be energized.
    When switched to idle position then run and run/idle should only be energized.
    When switched to Run position then only run terminal should only be energized.
    When switched to start position then run and start terminal should only be energized.
    Remember at weld/auxiliary power speed turning off the ignition the engine will take a few seconds to spin down to stop(spinning mass)

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