Engine Trouble horrible knocking sound

Discussion in '2-Stroke Engines' started by cnewlight, Sep 23, 2014.

  1. cnewlight

    cnewlight New Member

    so now im here, i bought a new racing carburator for my 80 cc it came with a new throttle cable and 5 jets 60-80 i started with the 80 and ended up on the 60 jet it was fine... it was the one that made her go fast well after about ten min of riding at almost top speed i hear a knocking sound. it will stay running but i have not tested it to see if it will engage and actually ride im worried i blew my engine but my research has me to believe i have a piston problem should i buy a new one?
     

  2. jaguar

    jaguar Well-Known Member

    my god man, take it apart and see what is wrong.
    possibilities:
    1) you have too high compression and too lean a jet and you are causing pre-ignition
    2) the top connecting rod bearing has gone bad
    3) you have a new high compression head and the piston starts hitting it after it and the rod expand enough from heat
    4) you have a long spark plug and the piston starts hitting it after getting hot
     
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  3. Whiteride

    Whiteride Guest

    Agree with the above, take the cylinder head off and inspect the piston for any marking. That would be a good start to identify any problems, in no case run it any more until you have done an inspection.
     
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  4. butre

    butre Well-Known Member

    could be just overheating, a #60 is way lean. step it up one jet size after it cools down and test it.

    these engines often need to be a little rich for cooling purposes
     
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  5. cnewlight

    cnewlight New Member

    thanks jaguar for the reply and to the other guys... update: ive taken the top end off there is no damage to the piston or the cylinder head. one thing i have noticed is that the piston does have a lot of play going side to side i am not sure if its supposed to slide side to side like it does maybe i need to take the piston off and examin it? also my spark plug has always been fine with the engine never had a prob with it hitting could the b=new jet have caused this to happen? im going to start with jaguars post of #1-3 sgtarting with #1 and hope for the best!
     
  6. butre

    butre Well-Known Member

    all the pistons have massive side to side play. I'm still betting on overheating due to lean fuel/air mix
     
  7. cnewlight

    cnewlight New Member

    So this overheating could have ruined my piston?
     
  8. butre

    butre Well-Known Member

    it's not ruined unless there's a hole in it or big scores down the sides.
     
  9. Fabian

    Fabian Well-Known Member

    How hard did you rev the engine when going fast?

    How hot did the engine get?

    What oil/fuel ratio were you using?
     
  10. cnewlight

    cnewlight New Member

    I was abou full throttle when it started to knock I am using 50:1 and I'm not sure how hot it got
     
  11. Fabian

    Fabian Well-Known Member

    How hard was the engine revving when at full throttle?
     
  12. Fabian

    Fabian Well-Known Member

    :iagree:

    The engine currently in my bike needs a No 77 main jet to run optimally, with fuel that is equivalent to American 93 octane and an oil/fuel ratio of 25:1

    The previous engine needed a No 76 main jet.
    The engine previous to that needed a No 70 main jet.
    The engine previous to that needed a No 83 main jet.
    The engine previous to that needed a No 86 main jet.
     
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