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Thread: Question D4 Pony Motor Throttle spring loaded to be at full throttle?

  1. #1
    Join Date
    May 2019
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    Default Question D4 Pony Motor Throttle spring loaded to be at full throttle?

    My D4 pony motor throttle control has to be held by hand to keep at idle or below full throttle if I just release it goes to full set throttle. I cant set it without holding on to the throttle or it will spring to full throttle. Is this normal and if not what could be wrong or how can I fix it?

  2. #2
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    full throttle or Governed speed??? if it is running full throttle don't run it until it is fixed. most likely though it is just running at governed speed. the hand throttle just pulls against the governor to overcome the spring on the governor arm. mine has a small friction button on the throttle control that will hold at idle if i set it.
    D4 6U,1943 D4 2T,Laplant Choate C41 Carrimor Scraper

  3. #3
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    The governor spring wants to keep the throttle positioned such that the pony maintains governed rpm, which is about 3000rpm. So, the throttle rod is "fighting" against this. There is a spring bearing on the throttle and choke rods that is supposed to help the throttle rod maintain its position. However if the rod is lubed, or the spring is weak, it won't be able to, so the governor spring eventually pulls the throttle rod back into high idle position. Clean up the throttle rod, do not lube it, and check that the spring is sufficiently firm to hold it in place. If not, swap it out for a stronger spring
    Cheers,
    Neil.

  4. #4
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    Thank you bursitis and Neil. I will look into the spring between the two throttle and choke to try and get a bite on them so they will hold. Where would I adjust the governed speed, is it the set screw? The pony motor seems to be running a bit more like 4k instead of the 3k everyone talks about.

  5. #5
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    The governed speed is set by the linkage length connecting the gov to the carb.
    D2 5u & 3J
    212 9T
    RD4
    D4 7J & 7U
    R4 4G
    Gas 35's
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  6. #6
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    I always thought you adjusted the high speed by changing the tension on the governor arm spring that pulls the throttle open. More tension equals higher rpm. At least thats how most other simple governors work. Adjusting governor-throttle linkage length is usually done to fix "hunting".
    D2-5J's, D6-9U's, D318 and D333 power units, 12E-99E grader, 922B & 944A wheel loaders, D330C generator set, DW20 water tanker and a bunch of Jersey cows to take care of in my spare time

  7. #7
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    Quote Originally Posted by ccjersey View Post
    I always thought you adjusted the high speed by changing the tension on the governor arm spring that pulls the throttle open. More tension equals higher rpm. At least thats how most other simple governors work. Adjusting governor-throttle linkage length is usually done to fix "hunting".
    Yes, think you are right. I dis-remenbered that, it's been a while I guess.
    D2 5u & 3J
    212 9T
    RD4
    D4 7J & 7U
    R4 4G
    Gas 35's
    Diesel 35
    Diesel 40
    Gas 50's 5A
    Diesel 50 1E1755
    Diesel 75
    D 8800 power unit 9J 6113SP
    LeTourneau D4 tournapull/Q Carryall
    Letourneau D Carryall's
    LaPlant-Choate CAB-97

  8. #8
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    Yes, it's the set screw adjusting the spring on the governor. I just put the tach on my pony and it's running 3170 high idle so I'll tweak it down a little
    Cheers,
    Neil.

  9. #9
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    Thank you, all the information shared has been very helpful. I'll adjust the high idle spring set screw and bring it down to the recommended spec of 3150 using my digital tach gauge. I think taking some of that spring tension off might help with my choke/throttle control spring back as well.

  10. #10
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    Default Photo of Throttle and Governer

    Hi All,
    Here is a photo of a pilot motor that i have done up for the 7U when the engine is rebuilt. As you can see it shows the linkages for the throttle, choke and governer (yes i know its not connected). On left you can see the buttons that hold the throttle in postion and on the right you can see the adjusting screw/nut for the governer.



    Regards
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    Daryl
    RD4 4G4368
    D4 7J9915SP
    R4 6G2554SP
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    D4 7U37855


    May you always be in the right place at the right time with a fist full of Dollars

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