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  1. #1
    Silver Member
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    Jul 2011
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    172
    Tractor
    Steiner 430

    Default Idles great but...

    Yesterday, I noticed something might be wrong with one of the cylinders. It appeared to be a loose plug wire.
    Today, I noticed I don't have much power. She idles nice. Sounds very strong. However when I step on the treadle she doesn't move too fast and the engine bogs down.

  2. #2
    Epic Contributor MossRoad's Avatar
    Join Date
    Aug 2001
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    22,775
    Location
    South Bend, Indiana (near)
    Tractor
    Power Trac PT425 2001 Model Year

    Default Re: Idles great but...

    So it idles nice.
    Then you throttle up. Does the engine run good at high throttle also?

    Then you try to move the tractor and it bogs the engine down?

    I would try raising all four tires off the ground and then operating the treadle to see if it moves the wheels with no load on them or if that bogs the engine as well.
    MossRoad

    Click On My Little Tractor
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  3. #3
    Elite Member BobRip's Avatar
    Join Date
    Sep 2004
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    4,191
    Location
    Powhatan Va.
    Tractor
    2000 Power Trac 422

    Default Re: Idles great but...

    Could be ignition. Pull off one ignition wire and see if that makes a difference. If it does not then the coil or spark plug on that side is bad. Then try the other side.
    Bob Rip
    Tell me and I will hear.
    Show me and I will see.
    Let me do and I will learn.
    Let me fail and I will understand.

  4. #4
    Silver Member
    Join Date
    Jul 2011
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    172
    Tractor
    Steiner 430

    Default Re: Idles great but...

    I just put it up on blocks. Didn't notice the engine bogging down. There was a lot of backfiring when I sped up the idle.

  5. #5
    Epic Contributor MossRoad's Avatar
    Join Date
    Aug 2001
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    22,775
    Location
    South Bend, Indiana (near)
    Tractor
    Power Trac PT425 2001 Model Year

    Default Re: Idles great but...

    Get the engine running good while its up on blocks first.
    Once you can attain high throttle with no problems, put it back down and see if the engine still functions good under load of driving.
    MossRoad

    Click On My Little Tractor
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  6. #6
    Epic Contributor MossRoad's Avatar
    Join Date
    Aug 2001
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    22,775
    Location
    South Bend, Indiana (near)
    Tractor
    Power Trac PT425 2001 Model Year

    Default Re: Idles great but...

    Quote Originally Posted by Frank Sorbello View Post
    Yesterday, I noticed something might be wrong with one of the cylinders. It appeared to be a loose plug wire.
    Today, I noticed I don't have much power. She idles nice. Sounds very strong. However when I step on the treadle she doesn't move too fast and the engine bogs down.
    O.K. Forgive me for asking, but I re-read your post.... you aren't expecting the engine speed to increase when you step on the treadle are you?
    MossRoad

    Click On My Little Tractor
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  7. #7
    Silver Member
    Join Date
    Jul 2011
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    172
    Tractor
    Steiner 430

    Default Re: Idles great but...

    No, when driving at full throttle she bogs down, treadle down all the way maybe going 3 mph. Something is wrong. Just can't figure what it is. A couple hours later I got on it and she acted normal for a few minutes. I thinking maybe something with the carburetor. What would cause it to repeatedly backfire while running?

  8. #8
    Platinum Member tmarks11's Avatar
    Join Date
    May 2005
    Posts
    634
    Location
    Port Orchard, WA
    Tractor
    2005 Power Trac 422

    Default Re: Idles great but...

    Quote Originally Posted by Frank Sorbello View Post
    What would cause it to repeatedly backfire while running?
    My guess is that you need to adjust your intake valve clearances (required every 500 hours of operation).

    Easy to do, will take about 15-30 minutes tops.

    Look at the service manual on page 38:
    http://robinamerica.com/media/manual...8968757500.pdf

    The only trick is how to get the engine to Top Dead Center (TDC), as the timing marks on the flywheel aren't viewable. Take out the spark plugs, and put a straw in the spark plug hole. Rotate the engine by brief bursts of the starter key until the straw shows that cylinder is at the top. That means you are either at TDC of the compression stroke (which is what you want), or the cylinder is at the top following the exhaust stroke (the exhaust valve will be open as the cylinder comes up).

    Could also be because your carburator is providing too lean of a mixture. Could be the carburator needs to be cleaned. I don't know how to adjust the mixture on the EH72, haven't had to do that yet.
    Last edited by tmarks11; 05-18-2013 at 08:06 AM.
    -----------------------------------------------------
    Now in Port Orchard, WA
    2005 PT-422
    4n1 bucket, minihoe, auger, 48" mower, land pride aerator, tow adaptor, forklift, crane, Herd GT77 spreader, LMB, 60" blade, M1 abrams turret.
    PT422 (6/23/05) photo page

  9. #9
    Gold Member Clumber's Avatar
    Join Date
    Sep 2010
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    348
    Location
    Northern Virginia
    Tractor
    PT425 (Dec 2010)

    Default Re: Idles great but...

    Quote Originally Posted by Frank Sorbello View Post
    No, when driving at full throttle she bogs down, treadle down all the way maybe going 3 mph. Something is wrong. Just can't figure what it is. A couple hours later I got on it and she acted normal for a few minutes. I thinking maybe something with the carburetor. What would cause it to repeatedly backfire while running?
    My PT-425 started doing that on a heavy work load day. It turned out to be bad spark plugs. When the engine became hot the plugs would not fire correctly causing backfire. Letting the engine cool down for 20 mins produced a normal run for about 1.5 hours until it heated up again. The electrodes on the plugs were whitish when hot. Installing new plugs solved the issue -- running normal now.

    Note that my Robin user's manual says the correct replacement plugs are NGK-BPR5ES. Jack's Small Engines site says NGK-BPR6ES. Manuals on the Robin support suggest different plugs. The plugs that came with the new tractor are NGK BPR4EY. A Robin tech support guy said I could use anyone of those. I did not like that answer. The Robin Director of Tech Support suggested the following:

    You need the Production number (PN) for you engine, located just above the serial number. For example for my PT-425 it is EH720DS00117112.
    Then go to the Robin Parts Catalog (ordered by Specification, that is, the Production number):

    https://euc.robin-fhi.co.jp/parts_ca...el.aspx?lang=e
    Look up the 1st 5 digits of your PN to get a list of productions for your engine. You will see blow up parts diagrams for that specific engine production.

    You can also Google the PN leaving out the last 4 digits. I found a site that has better prices than Jack's on several parts:
    Subaru / Robin EH720DS0011 Parts List and Diagram : eReplacementParts.com

    The correct spark plug for my engine is NGK-BRP4EY.
    I married me a hippy, ran away with a stringy haired blond,
    Now we're both old and happy, fishing on our own Golden Pond. -- Merle Haggard


    PT 425 (Dec 2010), Blade, Snow Blower, Sweeper, Spreader, LMB, 4n1, Small Bucket/Teeth, Utility Grapple, Brush Cutter, Box Blade, Mini Hoe/Thumb, Forks, Power Dumper

  10. #10
    Super Star Member murphy1244's Avatar
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    Nov 2011
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    16,361
    Location
    Ohio
    Tractor
    Kioti DK 40-Massey ferguson 135-Ventrac 4500 Diesel

    Default Re: Idles great but...

    try running some Sea foam in it before you change the plugs.
    Murph ------------

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