Home Forums Tech Talk KT100 HDC-5B clutch limits revs and gets hot

This topic contains 5 replies, has 6 voices, and was last updated by  Matt Dixon 4 years, 11 months ago.

  • Author
  • #28485

    Ron Horwitz

    New to kart clutches.  I took apart the HDC-5B clutch on my son’s KT100 kart, cleaned and inspected everything and put it back together.  It was behaving just fine before I disassembled.  I didn’t mess with the springs or hammers, just sprayed that assembly with brake cleaner and reinstalled it.  On the stand I can watch the clutch engage and the engine easily revs past 10k.  When my son gets in it, the clutch engages but then stops revving at 9000-9200 rpm and he can’t get it to keep accelerating.  After about 4 trips up and down the street, when he stopped there were wisps of smoke coming off of the clutch.  What did I do and how can I fix it?


  • #28506

    tony zambos

    If you truly only sprayed the clutch with brake cleaner and didn’t touch the spring adjusters, the clutch should be fine. Did you use the recommended tools to pull the clutch and reinstall it? I’d pull the clutch again to see if anything has broken. Revving the engine on the stand is not going to give you an accurate indication of when the clutch locks up and the engine should rev way past 10k.
    If it’s not the clutch, you could have an engine or carb issue, or you have too small of a gear on the axle. If you keep running down the street having smoke coming off the clutch, stop doing both. Over heating the clutch is going to shorten the life span of the friction discs, floaters and springs.

    LAD Specialties customer / tony kart / rotax / kt100

  • #28514

    Gary Lawson

    When you say you disassembled it did you remove the disks and floater? If you did and you flipped any one of them then you are not getting full contact anymore. Brand new they are perfectly flat but once you run them they become concave. This is likely the issue. Only other option would be contamination with oil. The overheating issue is from excessive slipping. The “stop accelerating” at 9000-9200 sounds like you are describing the stall speed. Assuming it is a can engine it should be closer to 5
    8600. You should not do more than 2 clutch tests in a row without letting the clutch cool. Even if engagement is set correctly it will get very hot! The quick fix is to take a 1/4 turn counterclockwise from each spring to lower engagement. Assuming a plate is backward it will be hard to determine and correct now. Ifeal fix would be to get new disks and floater and have the clutch re machined flat with .030 air gap and start over.

  • #28535

    Walt Gifford

    I’ve seen clutches put together wrong where the drive hub isn’t lined up with the lever support.

    Going up and down a street is very hard on a clutch. 4 trips will burn the clutch almost from a standing start 8 times, not what it was designed for.


    FAA certified jet engine and aircraft technician,
    Nicholson Speedway class champion 2001,
    Yamaha KT100 Service Center,
    41 years karting experience

  • #28773

    Al Nunley

    First thing we would need to know is; what exhaust.  The can, three hole, 4 hole or a pipe all want different engagement rpm’s.

    Second thing we would need to know is;  is the engine blueprinted?   What are the CC’s in the combustion chamber?


    From the desk of Al Nunley
    Comments compliments criticisms and questions always welcome.
    If the data does not support the theory, get a new theory.
    (Al Nunley)

    From the desk of Al Nunley

  • #28801

    Matt Dixon

    Nice… correct me if Im wrong but is this Al’s first post on the new forum???


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