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Bobcat 225G Plus - Won't Idle Right

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  • Bobcat 225G Plus - Won't Idle Right

    I just bought a Miller Bobcat 225G Plus (1996 model or so). It starts and runs, but continuously idles up and down, up and down. It will also not run at weld speed when I turn the switch to "rabbit". Idles up and down regardless of switch position.

    I have done a complete tune up (plugs, wires, new gas, oil & filter, air filter, fuel filter, etc) and I have also replaced the throttle solenoid and the problem persists. It will even idle up and down (and the thottle linkage moves back and forth) with the throttle solenoid completely detached.

    Any suggestions on what to try next? Thanks.

  • #2
    Pop the top cover and replace the idle module, which is the firt thing you should have looked at.

    Comment


    • #3
      Thanks Cruizer.

      Is there a way to test the idle module before spending $300 on a new one?

      Comment


      • #4
        Follow the engine harness from the starter back, there will be a plug there. It reallllly likes to corrode. Might want to check it.


        And $300 is a little too high. Go to: www.miller4less.com

        No the unit is pull to idle. Unfortunately without a serial#, Its tough to diagnose. "!996" or so doesn't cut it...
        Last edited by cruizer; 07-23-2012, 05:18 PM.

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        • #5
          I will check the harness and price the idle module at miller4less.

          If you have more diagnosis tips....here is the serial #, etc.

          Miller Serial #: KG052667
          Engine serial/model decal is missing. But it is an Onan Performer 16.

          Comment


          • #6
            It may be that your engine RPM is out of spec. For that you'd need a meter that reads frequency(HZ)

            Stuff your probes into the 120 Duplex on your machine. What your after is 43HZ no load at idle. Your machine is probably way low

            and 62.5hz high idle no load.

            Also check your oil level. screw in type dipstick, don't screw it in and out to check.

            O-ring type, don't press it past the o-ring to check

            Comment


            • #7
              Thanks again Cruizer. I think low RPM may be the problem, now that you mention it. It acts like a "governor" of some type is kicking in to rev it up and then it idles back down. Thanks for the frequency specs. That helps a lot b/c the docs I have say low idle should be 2200 RPM. But I have no way to measure RPM at this time. But I can check freq. I'll let you know what I find.

              Comment


              • #8
                All welders having AC auxillary are tuned this way, its more exact.

                Gassers are ALWAYS 43 low and 62.5 high

                Diesels are ALWAYS 39-43 low and 60.5 high,

                Lincoln diesels especially Vantages must be turned down, otherwise waveforms are out to lunch.

                Comment


                • #9
                  Originally posted by jallen View Post
                  It will even idle up and down (and the thottle linkage moves back and forth) with the throttle solenoid completely detached.
                  Then the problem definitely isn't the idler control module. Based on your description, you're on the right track to suspect the governor and likely looking at a governor sensitivity (governor lever spring hole location) issue. There's a possibility it could be carburetor but start with the sensitivity adjustment first. Also make sure the light tension spring is in place on the throttle link as this removes slack in the linkage that can otherwise result in slight speed fluctuations at weld/power speed.

                  If you don't have it, here's http://www.millerwelds.com/om/o403c_mil.pdf the correct manual for your unit SN.

                  If you PM me an email address, I can send you the engine manual for the P216 as well.

                  Comment


                  • #10
                    Thanks Duaneb55. Making progress, but the saga continues. Spent all day Saturday working on it in 101 degree Texas heat. Can't find my freqency meter, but did find an old tachometer. Sprayed carb cleaner into the air intake, re-adjusted the governer sensitivity (moved spring into a new hole) and took the slack out of throttle link that runs to the carb butterfly. I finally got the slow idle set pretty close to 2200rpm and it does NOT idle up and down at slow idle any more, but it does not run as smooth as I think it should. I think it idles a little rough. The engine is now finally responding to the idle control switch. When I put it on "rabbit" it idles up like it should (and close to the 3700 rpm the maunal calls for after I readjusted it), but it still "hunts" up and down, up and down on high idle. B/t 400-500 rpm or so.

                    Also, now that I have the slow idle set, I tested voltage at receptacles and tried to weld. A/C volts on slow idle are like 30 (way low) and it will not respond (rev up) when a load (grinder) is put on it. Also will not come up to weld speed when trying to throw an arc. It will weld, if i turn it to "rabbit", but engine still hunts so it's not a smooth arc.

                    Other things I've checked: The light tension spring is in place on the throttle link (thanks again duaneb55), fuse F1 and F2 are good, accelerator pump on carb sprays extra gas into carb when it does hunt (to bring engine speed up), I get 12 volts to the throttle solenoid when the switch is on "turtle/rabbit" and none when i put it on "rabbit".

                    Any other advice would be greatly appreciated. I think I'm close, but I'm running out of ideas.

                    Comment


                    • #11
                      Thanks to Duaneb55 for sending me the Onan engine manuals. I went through the troubleshooting guides and addressed all the possible issues that would cause "governor hunting". Turned out to be the carburetor. I torn it down, literally poured sandy material out of the bowl, cleaned all ports, etc and re-assembled. Cured the governor hunting and idle problem. Thanks again Duane and Cruizer for all the help!

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