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Tecumseh HM100 governor setup

Discussion in 'Mechanic and Repair' started by crabby grass, Dec 22, 2017.

  1. crabby grass

    crabby grass LawnSite Member
    Messages: 8

    I recently picked up a well used chipper with a HM-100 engine. It starts up fine but once off choke, it wants to take off and over-rev. I shut the machine down, lubed the governor linkages, and noticed that tension from the governor shaft wants to bring the throttle to the WOT position. When the engine is running the throttle is pegged open just like when the engine is off. I can use my finger to force the throttle back down but it speeds back up as soon as I release. Is there a missing spring or other mechanism that brings the throttle back to the closed position? Is this a sign that the governor is kaput?
     
  2. BigFish

    BigFish LawnSite Fanatic
    Messages: 5,898

  3. OP
    OP
    crabby grass

    crabby grass LawnSite Member
    Messages: 8

    There's only a fixed linkage that runs from the governor arm to the throttle control lever. I compared it to the closest setup I could find in the manual and it too doesn't show a link. Would it hurt to swap out the linkage with a spring?

    Resized_20180115_143012_4426.jpg

    Resized_20180115_143026_2935.jpg

    hmsk80-100.JPG
     
  4. BigFish

    BigFish LawnSite Fanatic
    Messages: 5,898

    Well, the gov.arm has to work against a spring. Has to.
    On yer motor the spring is located at the throttle control lever assy. The assy should be two separate pieces on a common pivot point. Should be able to look up parts here : http://www.mymowerparts.com/pdf/Tecumseh-Engine-Parts-Manuals/
    Ya might try google fer a more clear parts cut.
    Actually, I gotta go finish a tiller with the same setup so I'll try and take some pics and post em later today/tonight.
    I replaced the gov. internals and have to bolt it back on the tiller. I had to order the spring I'm talkin' about
     
    hort101 likes this.
  5. ricky86

    ricky86 LawnSite Silver Member
    Messages: 2,443

    The internal gov should try to close the throttle, not open it. The spring try's to open it. The balance is the governed top no load speed.
    When you make the initial adjustment, you pull the linkage so the throttle is wide open, and pull the gov lever adjustment the same way. If done correctly, the throttle will open and shut easily, static. You're opening the throttle and closing the spool. When the engine starts, the weights in the spool fly out and close the throttle.
    The linkage looks correct. Sounds as if you have an internal problem.
     
  6. BigFish

    BigFish LawnSite Fanatic
    Messages: 5,898

    Well, the unit I was workin' on is a HH40 , and not much is the same as on the 100, so no pics.
    After lookin at various parts cuts , none seem to show a gov spring. The only thing I can think of is the gov spring might be a torsional type that is acting on the throttle control arm that is connected to the gov arm and is part of the control assy. If so, could be all that crud/dirt is inhibiting the spring action or mayhaps jammin' up the lever.
    As was mentioned, could also be the internal gov. gear/spool assy. That is what went south on the unit I was talkin about.
    Partstree has several diagrams, ya gotta have yer spec number. Example :
    http://www.partstree.com/parts/tecu...0-159272m-tecumseh-4-cycle-horizontal-engine/
     
    Last edited: Jan 23, 2018
  7. OP
    OP
    crabby grass

    crabby grass LawnSite Member
    Messages: 8

    The throttle always wants to be in the open position even when the engine is off. It was like that since I bought it used last year. The first thing I did when it over-revved was to clean and lube all the governor and throttle linkages. That didn't work so I jury-rigged an opposing spring to keep it closed. I turned up the idle speed screw a bit and manually worked the throttle since I had a lot of brush to chip. So the consensus is the governor internals are kaput?
     
  8. BigFish

    BigFish LawnSite Fanatic
    Messages: 5,898

    That is how most governors work, the spring holds the carb throttle plate open, even when off. Start it up, it wants to rev, as mentioned, the internal gov. wants to close it.

    Is there a spring? sounds like there is. If you did a static gov. adj. and still not acting right, then ya prolly got an internal problem.
     
  9. OP
    OP
    crabby grass

    crabby grass LawnSite Member
    Messages: 8

    There isn't a spring, just a hard/rigid link. I tried adjusting the governor per the manual, so looks like its the governor then. Thanks for the help guys.
     
  10. Nelson M Martin

    Nelson M Martin LawnSite Member
    from Ontario
    Messages: 244

    i think in your first picture there is some kind of spring just below the intake fastening screw
    But my small knowledge would only make this a constant rpm engine if no throttle cable attached
     

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